Reaction of Thiols

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 3, pp. 319–346. © Pleiades Publishing, Ltd., 2007.Original Russian Text © I.V. Koval’, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 3, pp. 327–351. REVIEW Reactions of Thiols I. V. Koval’ Ukrainian State University of Chemical Technology, pr. Gagarina 8, Dnepropetrovsk, 49005 Ukraine Received May 10, 2003 Abstract—Published data on the reactivity of thiols, specifically C-, N-, P-, and S-sulfanylation reactions, halogenolysis of S–H bond, dealkylation, and oxidation, are reviewed. DOI: 10.1134/S1070428007030013 1. Introduction ............................................................................................................................................... 2. C-Sulfanylation ......................................................................................................................................... 2.1. Replacement of Halogen at a Carbon Atom by RS Group .................................................................. 2.2. Replacement of Other Atoms and Functional Groups by RS Group ................................................... 2.3. Addition of Thiols at Multiple Bonds of Unsaturated Compounds ..................................................... 2.4. Ring Opening by the Action of Thiols ................................................................................................ 3. N-Sulfanylation ......................................................................................................................................... 4. P-Sulfanylation ......................................................................................................................................... 5. S-Sulfanylation ......................................................................................................................................... 6. Halogenolysis of S–H Bond and Formation of S-Nitroso Derivatives ..................................................... 7. Dealkylation with Participation of Thiols ................................................................................................. 8. Reactions of Thiols Involving Cleavage of the C–S Bond ....................................................................... 9. Transformations of Thiols by the Action of Oxidants ............................................................................... 319 320 320 327 328 334 336 336 337 337 338 339 339 1. INTRODUCTION All chemical processes occurring with thiols may be divided into the following groups with respect to the character of changes in their molecules: reactions involving cleavage of the S–H bond; reactions involvIvan Koval’ was born in 1942 in Podgorodnoe village, Dnepropetrovsk region. In 1967 he graduated from the Dnepropetrovsk Institute of Chemical Technology; Candidate of c h e mi ca l s ci en ce s s in c e 1 9 7 0, Doctor of chemical sciences since 1987; In 1995, I. Koval’ was elected a Full Member of the Ukrainian Academy of Technology. I. Koval’ is now head of the Department of Chemical Technology of High-Molecular Compounds at the Ukrainian State University of Chemical Technology, Dnepropetrovsk, Ukraine. Fields of scientific interest: organoelement chemistry and chemistry of high-molecular compounds. I. Koval’ discovered, developed methods for generation, and thoroughly studied properties of α-sulfenyl N-centered anions. He is author of more than 200 publications, including 20 reviews on modern problems of organoelement chemistry. ing cleavage of the C–S bond; reactions accompanied by change of the oxidation state of the sulfur atom; and heterocyclizations. It should be emphasized that each of these groups includes a variety of transformations which cannot be covered to a sufficient extent in the framework of a single paper; therefore, the present review deals only with the first three groups of thiol reactions. Reactions involving cleavage of the S–H bond are especially diverse. The ease of dissociation of the S–H bond in thiols is directly related to its energy which is estimated at 82–94 kcal/mol [1]. Depending on the conditions and thiol nature, heterolytic dissociation of the S–H bond to give thiolate anion or sulfanyl cation or homolytic dissociation with formation of sulfanyl radicals can occur, and these species can directly participate in various transformations. Processes accompanied by cleavage of the S–H bond primarily include those resulting in introduction of an RS fragment into organic molecules. Such reactions are generically called sulfanylation (thiylation). Depending on the bond being formed, C-, N-, P-, S-, and Si-sulfanylation may be distinguished. In the recent years, sulfanylation reactions have been exten- 319 320 KOVAL’ sively used in preparative organic chemistry and chemistry of natural compounds. These reactions underlie a number of preparative methods for the synthesis of sulfides [2, 3], disulfides [4, 5], and sulfenamides [6, 7], including biologically active compounds [8], as well as for introduction of acid-labile protecting groups into molecules of sulfur-containing amino acids and proteins [9, 10] and deprotection [11–15]. 2. C-SULFANYLATION C-Sulfanylation is based primarily on replacement of halogen atoms and other functional groups at a carbon atom by RS group, addition of thiols at multiple bonds of unsaturated compounds, and opening of unstable rings by the action of thiols. 2.1. Replacement of Halogen at a Carbon Atom by RS Group Replacement of a halogen atom by an RS group occurs in reactions of thiols with various halogen derivatives. Replacement of a halogen atom at a saturated carbon atom by an RS group has long been known and extensively studied; as a rule, it follows a bimolecular mechanism, and d orbitals of the sulfur atom participate in stabilization of the transition state. Several procedures for performing such reactions have been developed. The most widely used version implies heating of a mixture of appropriate thiol and halogen derivative in a polar solvent (aqueous alcohol, alcohol, acetone, DMF, DMSO, etc.) in the presence of an alkali. For example, benzenethiol [16, 17], 1,3-benzothiazole-2-thiol [18], benzimidazole-2-thiol [18], and 1,3-benzoxazole-2-thiol [18] were alkylated with ethyl chloroacetate, while 5-methyl-1,3,4-thiadiazole-2-thiol was alkylated with ethyl bromoacetate [19] with a view to obtain new antimicrobial agents (Scheme 1). The reactions were carried out by heating the reactants in boiling acetone in the presence of K2CO3. Chloromethylation of 1,3-benzoxazole-2-thiol was performed under analogous conditions [20]. The reaction of bis(2-chlorocyclohexyl) sulfide with benzenethiol gave bis(2-phenylsulfanylcyclohexyl) sulfide as a mixture of stereoisomers [21]. Scheme 1. RSH + XCH2COOEt Me2 CO, K 2CO3 RSCH2COOEt A number of symmetric and unsymmetric sulfides were synthesized using acetone, dimethylformamide, or their mixture as solvent in the presence of K2CO3 [22–24] (Scheme 2). The reactions were activated by ultrasonic [22] or microwave irradiation [23]. Scheme 2. RSH + R'X RSR' R = Bu, PhCH2, HOCH2CH2, Ph, 4-ClC6H4, 2-HSC6H4; R' = Pr, i-Pr, Bu, PhCH2, C12H25; X = Cl, Br. Sodium hydroxide is used very frequently as hydrogen halide acceptor, e.g., in the replacement of the chlorine atom in the chloromethyl fragment of nucleosides by benzylsulfanyl group [25] (Scheme 3). Scheme 3. O N ClCH2 N N N N R + PhCH2SH O N NaOH, DMSO Ph S N N HO O N N R R= HO OH . In some cases, aqueous–alcoholic [26] or aqueous solutions [27–30] of NaOH are used instead of solid alkali, and sulfanylation in aqueous medium is carried out in the presence of phase-transfer catalysts [27, 28, 30]. Replacement of one chlorine atom in 1,2-dichloroethane [27] and 1,1-dichloro-2-chloromethylcycloScheme 4. PhSH + ClCH2 CH2Cl Cl PhSH + Cl Cl Et3 NBzl Cl– PhSCH2CH2Cl Cl S Cl R = Ph, 1,3-benzothiazol-2-yl, 1,3-benzoxazol-2-yl, 1H-benzimidazol-2-yl, 5-methyl-1,3,4-thiadiazol-2-yl; X = Cl, Br. Et3NBzl Cl – Ph RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 3 2007 R2 = H. The third version makes use of alkali metal thiolates that are brought into reaction with halogen derivatives. An example is the synthesis of 1-(1-phenylsulfanylbutyl)-1H-benzotriazole RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. Cl. EtOCO. reflux ArSCH2COOR MeO R = Quinolin-8-yl. Et. the bromine atom in ethyl 4-bromobut-2enoate was replaced by benzylsulfanyl group in the presence of triethylamine [33] (Scheme 6). N N N Me Cl + PhSNa N MeOH. PhH. Br. as a rule in alcoholic medium. etc. Ar = 4-MeC6H4. the benzylic chlorine atom in 7-(4acetyl-2-chloromethyl-5-hydroxyphenoxy)heptanenitrile was replaced by methylsulfanyl group in chloroform in the presence of triethylamine [32] (Scheme 5). 4-ClC6H4. Scheme 6. Et3 N. Halogen atoms in polyfluorohaloalkanes were replaced by RS groups by heating with the corresponding sodium Scheme 10. Me. .REACTIONS OF THIOLS 321 propane [28] by phenylsulfanyl group was performed in aqueous–alcoholic medium in the presence of benzyltriethylammonium chloride (Scheme 4). [31] used modified bentonite clays to catalyze reactions of thiols with benzyl chlorides. Kannan et al. Et. Scheme 9. CH2 Cl R3 NaS OH COMe + COOR1 R3 Et3 N. 43 No. pyridine. 20°C N N Me Ph S Replacement of the chlorine atom in methyl and ethyl 3-chloromethylbenzoates by arylsulfanyl groups was performed under analogous conditions [36] (Scheme 9). such as triethylamine. ArSH + ClCH2 COOR Pyridine PhH. MeOCO. etc. O O OMe R EtOH MeO R SR' OMe Br O O + KSR' Scheme 7. Scheme 5. reflux R O O 1 S R2 Likewise. while the chlorine atom in quinolin-8-yl chloroacetate was replaced by arylsulfanyl groups in the presence of pyridine [34] (Scheme 7). According to the second procedure for replacement of a halogen atom at a saturated carbon atom by RS group. PhCH2SH + BrCH2CH=CHCOOEt R1 = Me. COMe OH + MeSH ClCH2 O(CH2 )6 CN by reaction of sodium benzenethiolate with 1-(1-chlorobutyl)-1H-benzotriazole in methanol [35] (Scheme 8). 19 h MeS R2 O(CH2) 6CN MeOH. 3 2007 R = Phthalimido. HOCO. MeO. For instance. reactions of thiols with halogen derivatives are performed in anhydrous organic solvents in the presence of organic bases. R' = Me. 5°C. R3 = H. Scheme 8. C6H13. reflux PhCH2SCH2CH=CHCOOEt An important step in the synthesis of 4-R-sulfanyl derivatives of glutamic acid [37] is the reaction of the corresponding bromo derivative with potassium thiolates in alcoholic medium (Scheme 10). PhSH + BrCH2 CH=CH2 EtONa EtOH. H(CF2)6CH2. I. p-C6H4C6H4-p. RSNa + R'X PhH. N 2 S N SCH2 XCH2 S S S N SNa + ClCH2 XCH2Cl R R' NO2 EtONa.3-benzoxazol-2-yl. 18°C CH3SCH2 CH2 OH Ethanolic sodium ethoxide was used to effect substitution of the chlorine atom in benzyl chloride and its derivatives by arylsulfanyl groups [41] (Scheme 14). Reactant mixtures were heated in DMF at 130– 135°C (Scheme 12). Cl.3. [39] reported on the synthesis of bissulfides from sodium 1. Reactions of thiols with halogen derivatives in alcoholic medium in the presence of metal alkoxides may be regarded as a modification of the third procedure. Scheme 13. 4-ClC6H4. 20°C Cl SCPh3 methylsulfanyl group also occurs in methanol in the presence of sodium methoxide [45] (Scheme 18).4-dihydro-2H-1. Ph N R N S Ph EtONa. Ph. Me. NO2 SH + CH2Cl R = Me3 – m(MeO)mSi(CH2)n (m = 2. 18°C R S R' R = H. EtOH R N S N N CH2SR' N CH2 Cl + R'SH X = p-C6H4. Ph. p-C6H4CH2C6H4-p. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. i-Pr. Br + Ph3CSH Cl MeONa MeOH. Taber and Meagley [40] described the synthesis of 2-chloroethyl [13C]-methyl sulfide in which one step was the reaction of [13C]-methyl iodide with 2-sulfanylethanol in ethanol in the presence of sodium ethoxide (Scheme 13). Replacement of the chlorine atom in bicyclo[4.2. thiolates in boiling benzene [38] (Scheme 11). H(CF2)4CH2. 20°C O H Scheme 18. EtOH. X = Cl.3-benzothiazole-2-thiolate and bis-chloromethyl derivatives of aromatic hydrocarbons. EtOH. Mesropyan et al. R' = Pr. C6H11. Br. R' = H(CF2)2CH2. 1. 1. Scheme 12. as well as alkylation of benzenethiol with allyl bromide [42] (Scheme 15). MeO. 20°C PhSCH2 CH=CH2 Scheme 16. 43 No. 3 2007 . n = 1–3). 3. A number of 4-R-2-(R'methylsulfanyl)-5-phenyl-3.3-benzothiazol-2-yl. Selective replacement of the bromine atom in 1-bromo-3-chlorocyclobutane by triphenyl- t-BuOK. Scheme 17. R' = H.0]nonane derivative by phenylsulfanyl group was carried out in methanol in the presence of potassium tert-butoxide [44] (Scheme 17). O H Cl + PhSH H H SPh CH3 I + HSCH2 CH2OH 13 EtONa. reflux RSR' KOVAL’ Scheme 14. MeOH. Scheme 15. 2-pyridyl.322 Scheme 11. 13 R = Me.4-triazole-3-thiones possessing fungicide activity were synthesized by heating the corresponding chloromethyl derivatives with thiols in a boiling solution of sodium ethoxide in ethanol [43] (Scheme 16). The nature of thiol can also affect the product structure. R Cl 2 323 R 1 R2 + R3 SH R3S R1 + SR3 R2 R3S SR3 R1 O R1 = Me. The authors presumed [46] that the first stage of this process is nucleophilic replacement of chlorine by alkylsulfanyl group to give alkylsulfanyl ketones. Scheme 22. and it follows SRN1 radical ion mechanism [1. benzenethiol reacts with 1. for such halogen derivatives are inert toward thiols or thiolate ions. O Cl + RSH ( )n ( )n RS SR R = Et. As a rule.bis(alkylsulfanyl)alkenes [46] (Scheme 19). I2–SO2. fairly severe conditions are necessary to enable these reactions to occur. [46] examined reactions of α-chloro ketones with alkanethiols and found that the product structure depends on the nature of initial α-chloro ketone.. Bu. nucleophilic substitution can be accompanied by side processes leading to different products. e. The reaction is initiated by UV irradiation.g. RS – + R'F I RS + [R' I] · F [R' I] · F · RS– + R' F · R'F [RS · + R'F ] + I– [RSR' · ] F [RSR' · ] F + R' I F RSR' F + [R' ] · F R = Alk.and trans. For example.REACTIONS OF THIOLS Scheme 19. R3 = Et. 3 2007 . Me.2-bis(alkylsulfanyl)cycloalkenes were obtained from cyclic α-chloro ketones (Scheme 20). n = 1. C8F17. while only cis-1. Ar. EtOC(O)CH2. Bu. 43 No. as illustrated by Scheme 21 [47]. 2. Pr. Acyclic α-chloro ketones gave rise to mixtures of isomeric cis. Scheme 21. 48. 49] (Scheme 22). Scheme 20. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol.and trans-1-chloro-2-phenylsulfanylethylenes at a ratio of 1 : 1 [51] (Scheme 23). and they follow either radical or elimination–addition mechanism. Replacement of a halogen atom at an unsaturated carbon atom (in olefins and acetylene derivatives) by RS group is a relatively rare case. R' = C3F7. addition to the latter of the second thiol molecule leads to the corresponding alkylsulfanyl-substituted alcohols which lose water molecule under acidic conditions to form the final products. Some systems. EtOH CH2 CH2=CHCH2SH O S CH2 O O SBu O S If a halogen derivative contains other functional groups capable of reacting with thiols. facilitate perfluoroalkylation of thiols [50]. It is seen that the reaction with butane-1-thiol gives the corresponding nucleophilic substitution product and that unsaturated sulfide is formed in the reaction with prop-2-ene-1-thiol.2-dichloroethene in the gas phase at 450–500°C according to radical mechanism to produce a mixture of cis. R2 = H. BuS Cl O S BuSH Cl O EtONa. A specific case of nucleophilic replacement of a halogen atom at a saturated carbon atom by RS group is the reaction of perfluoroiodoalkanes with thiols. Mursakulov et al. Replacement of a halogen atom in aryl halides by RS group is facilitated when the aromatic ring contains strong electronwithdrawing groups (such as NO2.) in the ortho or para position with respect to the halogen atom. Cl F F + 2 HSCH2CH2OH F F S CH2 Cl NaOH. the reaction of 6-chloro-1. In these cases. the reactions are carried out by heating an appropriate aryl halide with sodium thiolate in alcoholic medium.4-dinitrobenzene [9] (Scheme 25).3-dithiol and hexane-1.. while the rate of replacement of fluorine is greater by about two orders of magnitude. Cu2O. and it weakens in the series F > Br > Cl [55]. I.e. [55] previously reviewed methods for replacement of halogen atoms in an aromatic ring by RS groups.and (Z)-bis(ethylsulfanyl)ethenes. These reactions have found wide application in bioorganic chemistry for the introduction of protecting groups and various labels into peptide and protein molecules possessing HS groups.2-trichloroethylene with benzenethiol in alcoholic medium in the presence of sodium ethoxide on heating for 12 h under reflux [52]. 3 2007 .5tetrafluoro-3-vinylsulfanylbenzene with 2-sulfanylethanol in DMF in the presence of NaOH at room temperature results in replacement of two fluorine atoms rather than of the chlorine atom [58] (Scheme 26). 57]. PhSH + ClCH=CHCl 450–500°C PhSCH=CHCl KOVAL’ (E)-1. where one step involved replacement of chlorine at an unsaturated carbon atom by RS group (Scheme 24).1. The rates of replacement of Br.4.2-Dichloro-1-phenylsulfanylethylene was obtained in 63% yield by treatment of 1. etc. strong base) according to the elimination–addition mechanism (Scheme 28).324 Scheme 23.3-diene in alcoholic alkali to give mixtures of products as a result of nucleophilic substitution of the terminal chlorine atoms [54]. These data indicate that polarization of the carbon–halogen bond (more exactly. [53] described a one-pot twostep synthesis of (Z)-bis(methylsulfanyl). The most frequently used reagent is 1-fluoro-2. Nonactivated aryl halides [60–63] react with thiolate ions under more severe conditions (elevated temperature. Scheme 26. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. i. Et. In some cases. therefore. electron deficiency of the carbon atom attached to halogen) is the determining factor in this process.6-dithiol react with hexachlorobuta-1. and Cl differ insignificantly. F SH H N O + NO2 N H NO2 F S S CH2 HN O NH O 2N S NO2 Rybakova et al. Propane-1. ClCH=CHCl + 2 NaNH 2 ClC CNa ture till 1990. Bjorlo et al. Scheme 24. the process was accelerated using copper compounds (Cu. The sulfanylation process follows the SN2Ar bimolecular mechanism involving formation of intermediate σ-complex which is stabilized due to participation of the electron-withdrawing group and d orbitals of the sulfur atom. Scheme 25. only more recent publications are considered in the present review. when the latter is activated [56. The reactivity of activated aryl halides toward thiolate ions depends on the halogen nature. Much attention is given to halogen replacement by RS groups in the benzene ring of aromatic hydrocarbons. Therefore. 43 No. EtOH –2 EtONa –2 NH4Cl RSCH=CHSR R = Me.2. CN. DMF HO S F OH 2 RSNa. the review covered the relevant litera- Reactions of 4-fluoro-1-nitroanthraquinone with arenethiols also involve replacement of the fluorine atom by arylsulfanyl group [59] (Scheme 27). Ar. 4-MeC6H4. Ar = 2-HOCOC6H4. t-BuO–. Scheme 28. MeOH Cu2O. Scheme 29. etc. 43 No. The system DMF–K 2 CO 3 –Cu–KI was used to replace the bromine atom in 2. 4-MeC6H4. replacement of the latter by RS group occurs under milder conditions. Ht. 5 h S S SMe RS– RSH X = Cl. O F 325 + ArSH thiols in boiling toluene (reaction time 4–6 h) in the presence of phosphazenes and copper(I) bromide (Scheme 31). reflux. For instance. O NO2 O SAr ArI + Ar'SH Toluene. 4-Me. 4-MeC6H4. the yield of diaryl sulfides was 91 to 100%. 4–6 h ArSAr' K2CO3.4-Me2C6H3.3-dithiane (an analog of charatoxin) by treatment of 5-chloro-1.N-dimethylacetamide for 24 h [72] (Scheme 33). Mitsudera et al. The replacement of one bromine atom in 3. these reactions are usually performed to obtain new biologically active substances. S Cl + MeSNa S MeOH.and 4-bromotoluenes by ArS groups [61] (Scheme 30). 2 CuBr. [71] synthesized 5-methylsulfanyl-1. reflux + ArSH R R SAr R = 2-Me. 2-chloropyridine was converted into 2-arylsulfanylpyridines by heating with the corresponding sodium arenethiolate in ethanol–N. 24 h + ArSNa N Cl N SAr Ar = 2-MeC6H4. [63] synthesized a series of unsymmetric diaryl sulfides by reactions of the corresponding aryl iodides with areneScheme 30. Ar' = 4-ClC6H4. EtOH–DMA reflux. X B– HX SR SR + RS– A relatively large number of studies [64–70] deal with nucleophilic substitution of halogens in various heterocyclic compounds by RS groups. Scheme 33.REACTIONS OF THIOLS Scheme 27. B– = MeO–. COOH Cl + ArSH MeONa.5-Me2C6H3. Scheme 32. According to the authors [63]. For example. NH–. 3. O NO2 Ar = Ph. 4-O2NC6H4. Br.) as catalyst. Scheme 31. The reaction was accompanied by formation of 3-bromo-5-(but-1-en-1- RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 2-Chloropyridine-3-carbonitrile [73] reacted with sodium thiolates in the presence of sodium methoxide or KOH at 20°C (3–4 h). while analogous reactions with 6-R2-4-R1-2-chloropyridine-3-carbonitrile [74] required heating for 12–14 h at 60–65°C (Scheme 34). If an electron-acceptor group is present in the pyridine ring together with halogen atom. F. KI 18 h. reflux. 3 2007 . I.3-dithiane with sodium methanethiolate in boiling methanol over a period of 5 h (Scheme 32). 180°C COOH SAr More severe conditions are necessary to replace a halogen atom in pyridine ring by RS group. 2. K2CO3. R = Alk. the chlorine atom in 2-chlorobenzoic acid was replaced by arylsulfanyl groups by heating the reactants in methanol in the presence of sodium methoxide and copper(I) oxide [61] (Scheme 29).5-dibromopyridine by vinylsulfanyl group to give 3-bromo-5(vinylsulfanyl)pyridine was effected under relatively mild conditions [75] (Scheme 35). Palomo et al. Cu. Br DMF. DMF Ar = Ph. Ar = Ph. CH2CH2C(O)Cl CH2CO2Me + PhSNa N ylsulfanyl)pyridine.326 Scheme 34. Ph. Many publications describe replacement by RS groups of halogen atoms in heterocyclic fragments of various natural compounds. Sulfanylation of 8-bromoadenosine [78] and steroids [79] with sodium methanethiolate and substitution of bromine and chlorine atoms in some mono. Br Br + CH 2=CHSNa N DMF.[80. The iodine atom in 5-iodopyridin2-amine is replaced by RS groups only in the presence of copper powder [76] (Scheme 36). Cu H 2N N SR CH2CH2C(O)SPh Benzene. Crooks and Copley [83] synthesized a series of CoA S-esters by acylation of sulfanyl groups in the latter with acyl chlorides (Scheme 37). With a view to elucidate the mechanism of action of 4-chlorobenzoyl coenzyme A dehalogenase. OH OH Bu-t RCOCl. HSCH 2XCH 2SH + 2 CH 2=C(Me)COCl KOH CH 2=C(Me)COSCH2XCH 2SCOC(Me)=CH2 X = CH2. Pr. R1 CN DMF R2 N SR3 4-XC 6H 4C(O)Cl + HSCoA Pyridine. 4-MeOC6H4. R1 CN + R SNa R2 N Cl 3 KOVAL’ Scheme 37. 4-benzylsulfanyl-3-nitrocoumarin was formed in quantitative yield. 4-MeC6H4. CH2(CH2CH2O)2. CH2SCH2CH2. 3 2007 . In the reaction of 4-chloro-3-nitrocoumarin with an equivalent amount of phenylmethanethiol. these reactions usually follow SN2 bimolecular mechanism. C5H11. reflux CH2CO2Me R = Me. Scheme 39. Scheme 38. reactions of acyl halides with thiols have been widely used in the synthesis and modification of various natural compounds. 45°C Br S CH2 Kumar et al. Scheme 35. Bis-sulfides interesting as potential biologically active substances were obtained from dithiols and methacryloyl chloride in the presence of potassium hydroxide and a phase-transfer catalyst [87] (Scheme 40). EtOCOCH2. Br. Carboxylic acid anhydrides are rarely used as acylating agents toward thiols [88. Scheme 36. n = 2–4. Bu. A multistep synthesis of steroid analogs included replacement of the chlorine atom in 3-(2methoxycarbonylmethylcyclohexan-1-yl)propionyl chloride by phenylsulfanyl group [85] (Scheme 38). while the reaction with 2 equiv of phenylmethanethiol gave 3.4-bis(benzylsulfanyl)coumarin [77]. I + RSNa H 2N N NaOH. In the recent years. 89]. Ph. PhH 4-XC6H4C(O)SCoA X = Cl. Scheme 40. R3 = Pr. [84] described a simple and convenient synthesis of 1-benzothiopyran-4-ones. 43 No. Et3N t-Bu t-Bu Bu-t (CH2)nSH (CH2)nSC(O)R R = Me. CH2OCH2CH2. A number of sulfides exhibiting antioxidant activity toward animal fats were synthesized by treatment of fatty acid chlorides with fatty–aromatic thiols in the presence of triethylamine [86] (Scheme 39). an important step in the synthetic sequence was replacement of chlorine in acyl chlorides by the 2-sulfanylbenzoic acid residue. 81] and disaccharides [82] by PhS and HS(CH2)3S groups were reported. R1 = R2 = H. Bu. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. F. Replacement of halogen atoms in acyl halides by RS groups has been studied in sufficient detail. 43 No.REACTIONS OF THIOLS 327 2. Several procedures were developed for this purpose. Replacement of various functional groups by RS moieties was reported much more frequently. HS COOH + NH2 Me O N H OH X is a peptide residue.1'-cyclohexane] by RS group (Scheme 41). The first of these is based on reactions of hydroxy compounds with thiols in the presence of a catalyst. The hydroxy group in 1-hydroxy-5-R-8-methoxytetrahydronaphthalene was replaced by ethoxycarbonylmethylsulfanyl group in the presence of zinc(II) iodide [95] (Scheme 45). the substitution process followed the addition–elimination (oxidation) pattern. OMe OH HSCH2COOEt. H2SO4 X COOH SMe R = Pr. Ph. 3-Acetyl-1-methoxyindole reacted with sodium methanethiolate to give the corresponding 2-methylsulfanyl derivative in 93% yield [91]. The reaction was carried out in aqueous acetonitrile in the presence of an acetate buffer. Obviously. S-Acetylaminomethylcysteine (which is widely used in peptide syntheses) was prepared from cysteine and acetamide in alcoholic medium in the presence of hydrogen chloride [9] (Scheme 42). MeOH. t-Bu. O HCl. replacement of acyloxy group by sulfanyl. 97] and allyl alcohols [98] by RS group. The second step of the process. Scheme 45. is usually carried out in the presence of a catalyst such as boron RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. ZnI2 OMe SCH 2COOEt R R R = H. 3-MeOC6H4. followed by treatment with Fremy’s salt. alcohol 4-ClC6H4CONHCH2SAr Ar = 3-MeC6H4. Scheme 43. Boron trifluoride–ether complex was also used to catalyze replacement of the hydroxy group in fatty–aromatic [96.e. in particular in the synthesis of thioglycosides. This version is especially widely used in the carbohydrate chemistry. hydrogen replacement in position 6 is also possible. MeO. the initial step is formation of α-amino acid ester which then reacts with methanethiol to give the final product. H N + RSNa N H Replacement of the hydroxy group in 4-chloroN-(hydroxymethyl)benzamide by arylsulfanyl groups was performed under analogous conditions [93] (Scheme 43). Scheme 42. many examples of hydroxy group substitution were described. [94] reported on the replacement of the α-hydroxy group in α-amino acid fragments of peptides by methylsulfanyl group in acetic acid in the presence of concentrated sulfuric acid (Scheme 44). Replacement of Other Atoms and Functional Groups by RS Group Replacement of hydrogen by RS group is a fairly rare reaction. Scheme 44. alcohol Me N H S COOH NH 2 The second procedure for the replacement of OH group by RS includes preliminary acylation of hydroxy compound with acyl chlorides or carboxylic acid anhydrides. Replacement of two hydrogen atoms in the quinoid ring of the antitumor antibiotic Quinocarcin by two RS groups was reported [92].3-dihydro-1H-spiro[benzimidazole2. 4-ClC 6H4CONHCH 2OH + ArSH HCl. [90] described substitution of 5-H in 2. in the reaction with 2 equiv of sodium thiolate. 2-pyridyl. followed by replacement of the acyloxy group by RS. Presumably. Primarily. Scheme 41. i. 25°C RS H N N H Repin et al.. Hazelton et al. X COOH + MeSH OH AcOH.2. 3 2007 . 1. trimethylsilyl [129]. 114].3. 2-tert-Butylsulfanylbenzaldehyde was obtained in 72% yield by heating 2-nitrobenzaldehyde with 2-methylpropane-2-thiol in dimethylformamide [120] (Scheme 49). One nitro group in m-dinitrobenzene is readily replaced by phenylsulfanyl group in dimethylformamide or dimethyl sulfoxide in the presence of potassium carbonate on heating to 90–170°C [118] (Scheme 47). Scheme 47.4-di-O-acetyl-L-rhamnal was replaced by acetylsulfanyl group [104].6-dinitrotoluenes were formed via selective replacement of the ortho-nitro group. O 2N Me EtONa. both ortho-nitro groups can be replaced [121].4. 2. dimethyl sulfoxide) containing LiOH.4. as a result. EtOH N N NO2 O2N Me N N H O2 N + RSH N SR Me N RS Replacements of alkyl(aryl)sulfonyl [125. or Likewise. amino acids [110–112]. Replacement of an activated nitro group in an aromatic ring by RS group has been studied relatively well [55]. NO2 CN + MeSH SMe trifluoride–ether complex. the addition process can follow nucleophilic. and the latter is brought into reaction with thiols or sodium thiolates. electrophilic. Addition of Thiols at Multiple Bonds of Unsaturated Compounds Thiols are capable of adding at double C=C bonds of unsaturated compounds to give various sulfides. the corresponding 2-alkyl(aryl)sulfanyl-4.6-Tetra-O-acetyl-3-Obenzyl-β-D -glucopyranose was thus converted into ethyl 2. KOH. and the subsequent isomerization gave the corresponding 5-sulfanyl derivatives [124] (Scheme 50). alkoxy [127. Abramov et al.6-tri-O-acetyl-3-O-benzyl-1-thio-β-D-glucopyranoside [99] (Scheme 46).and ethoxycarbonylmethylsulfanyl groups. and the benzoyloxy group in methyl benzoate was replaced by alkyl(aryl)sulfanyl groups [105] in the absence of a catalyst. AcO PhCH2O CH2OAc O AcO t-BuOK. 108]. [123] synthesized 4-(m-carboran-9-ylsulfanyl)phthalonitrile in 62. nucleosides [109]. BF3 · Et2O AcO PhCH2O CH2OAc O AcO t-BuSH Thioglycosylation of other pyranosides was performed under similar conditions [100–103].4. The N-nitro group in 3-methyl-1. but such reactions are fairly rare. 100°C + SEt CHO SBu-t EtSH.6-Trinitrotoluene reacted with alkane. NO2 + PhSH NO2 K2CO3. the substrate is initially treated with sulfonyl chlorides or sulfonic acid anhydrides to obtain the corresponding sulfonate. This version was widely used in syntheses and transformations of antibiotics [106]. According to the third procedure for the replacement of hydroxy group by R-sulfanyl. 90–170°C NO2 SPh 2. OAc CHO CN DMF. This reaction occurs generally in polar organic solvents according to the SN2Ar mechanism. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 128]. 43 No. moth pheromones [107. and other natural compounds [115–117]. 3 2007 . Scheme 46.5% yield from the corresponding thiol and 4-nitrophthalonitrile in DMF in the presence of K2CO3 [123]. allylselanyl [130]. 20°C CN Scheme 49.2. carbohydrates [113.328 KOVAL’ Scheme 48. Depending on the reaction conditions.4-dinitropyrazole was replaced by phenyl. 2-nitrobenzonitrile reacts with methanethiol in dimethyl sulfoxide in the presence of potassium tert-butoxide to give 2-methylsulfanylbenzonitrile [119] (Scheme 48). The acetoxy group in 3.[121] or arenethiols [122] in dipolar aprotic solvents (dimethylformamide. Scheme 50. 126]. or K2CO3). In the reaction with 2 equiv of thiol. and trimethylammonio groups [131] by RS moieties have also been reported. and 1. SR' R SAr F3C H CF3SO3H. while β-trifluoromethylacrylic acid does not react with phenylmethanethiol even on prolonged heating.g.REACTIONS OF THIOLS 329 Scheme 53. C12H25. vinyl [144] and divinyl sulfones [145]. 3 2007 . Here. [148] studied electrophilic addition of various thiols at the C=C bond of α. H H CF3 + AcSH COOH CF3 AcS COOH C SR C BH+ Fast H C SR C + B 20°C Such organic bases as triethylamine [132]. Electrophilic addition of thiols at C=C bonds of unsaturated compounds occurs in acidic medium and involves intermediate formation of carbocationic species [9] (Scheme 53). 142]. H C C + H+ C C radical mechanism. as it was RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. Scheme 51. 120°C H + C 5H11SH COOH F 3C + C5H11S COOH COOH F3C SC5H11 R = H. The number of final products may also increase due to isomerization or disproportionation of primary adducts. Ar = 4-MeC6H4. yielding the corresponding β-acetylsulfanyl-substituted derivative (Scheme 55). 43 No. ketones [132. 135] and inorganic sodium [136] and potassium carbonates [137] are the most frequently used catalysts. esters [141. the reactions are performed with sodium thiolates [138] rather than with the corresponding thiols. F3C H H + AcSH COOH Δ F 3C AcS COOH Addition of phenylmethanethiol at the C=C bond of α-trifluoromethylacrylic acid occurs only at 100°C to give β-benzylsulfanyl derivative. In some cases. and the product was 3-acetylsulfanyl-2-trifluoromethylpropionic acid (Scheme 54). while in reactions with alkanethiolates nitro dithioacetals are formed as a result of subsequent addition of the second thiol molecule [147] (Scheme 52). Scheme 55. Nucleophilic addition of thiols to unsaturated compounds is a more common reaction. Scheme 52. R'SNa O 2N Ph R SO2C6H4Me-4 ArSNa O2 N Ph O2 N Ph SR' Thioacetic acid reacted with β-trifluoromethylacrylic acid on heating with exceptional regioselectivity. 1-Nitro-2-sulfonylalkenes react with arenethiolates to give products of replacement of the sulfonyl group. amides [137] and imides [143]. and piperidine [134. Thiols add relatively readily at polarized conjugated bond systems in unsaturated aldehydes [139]. Scheme 56. e.and β-trifluoromethyl-substituted acrylic acids. Vasil’eva et al. R' = Et. it is promoted by base catalysts which favor formation of thiolate ions. The rate-determining stage is the addition of thiolate anion to sp2-hybridized carbon atom [9] (Scheme 51).. 140]. Ph. 4-ClC6H4. An example is the addition of thiols to alloocimene in chloroform in the presence of BF3 · Et2O. The reaction of β-trifluoromethylacrylic acid with pentane-1-thiol under severe conditions leads to the formation of a mixture of two regioisomeric sulfides (Scheme 56).3-dinitrodienes [146]. Fast RSH + B RS– B + RSH H C C S H R H C C S R + H+ RS– B+ + C C Slow C SR C BH+ fluoromethylacrylic acid was accompanied by heat evolution. the nature of both thiol and unsaturated substrate is important. diisopropylamine [133]. which gives a mixture of three sulfides [149] (Scheme 57). Scheme 54. The addition of thioacetic acid to α-tri- Mixtures of several products are usually formed by electrophilic addition of thiols to unsaturated compounds having two or more double bonds. as a rule. and in some cases are not accompanied by undesirable side processes. hν RS· + H· C SR · C The authors presumed [157] that one-electron transfer between the initiator and perfluoroiodoalkane gives rise to perfluorinated radical species R·F which adds at the double bond of vinyl ether (Scheme 62). 1H-imidazol-1-yl. depending on the nature of acetylenic substrate. Scheme 57. Nucleophilic addition implies the presence of base catalysts favoring formation of thiolate ions as reactive species. Oxidative addition of benzenethiol and 2-methylpropane-1-thiol to styrene was performed under conditions of phase-transfer catalysis in the presence of peroxo complexes of transition metals [158]. and other factors. reflux.and β-adducts. CH2=CHCH2. solvent. Ph. and perfluoroiodoalkane in anhydrous diethyl ether was heated in the presence of PhSeNa or 4-MeOC6H4SeNa (Scheme 61). as well as of bis-sulfides (RS)2CHMe (R = Et. thiol. XCH=CH2 + BuSH AIBN. i-BuOCH=CH 2 + ArSH + R FI R = Et. Scheme 59. Apart from AIBN [155]. i-BuOCH=CH2 + R· F · i-BuOCH–CH2RF RS · H RSH C SR C + RS · ArSH –H · i-BuOCH(SAr)CH2RF Radical addition of thiols to olefins is usually characterized by a low energy of activation. Scheme 61. it follows a radical chain mechanism and is initiated by UV irradiation or radical initiators [151] (Scheme 59). RSH C C + PhSeNa. Ultraviolet irradiation was used to initiate photochemical addition of ethanethiol and its derivatives to ethynyl(vinyl)silanes [153] and of 3-(diethoxyphosphoryl)propane-1-thiol to 1-allyloxy-2. 2 h i-BuOCH(SAr)CH2RF Ar = 4-MeOC6H4. 43 No. Bu. OR + R'SH H 2C + Me OR CHO R'S SR' SR' + Me CHO O + SR' Me O CHO OR SR' OR of butane-1-thiol at the C=C bonds of 1-vinylpyrazole and 1-vinylimidazole at 20°C [initiated by azobis(isobutyronitrile) (AIBN) or UV light] yields 9–52% of the corresponding β-adducts [152] (Scheme 60). Radical addition of thiols at C=C bonds of unsaturated compounds is also well known. The addition of thiolate ion and the subsequent addition of proton may occur at both trans and cis position. PhCH2. therefore.3-epoxypropane [154]. Me. appropriate thiol. while radical perfluoroalkylarylsulfenylation of isobutyl vinyl ether was initiated by sodium benzeneselenolates [157]. electrophilic. Addition of thiols at the triple C≡C bond in acetylenic compounds can also follow nucleophilic. 3 2007 . In the latter case. as compared to ionic addition. other chemical initiators are frequently used. and radical mechanisms. radical addition Scheme 60. Rodin et al. i-Bu) [152]. a mixture of isobutyl vinyl ether. Scheme 62.330 KOVAL’ observed in reactions of thiols with 2-alkoxyprop-2enals [150] (Scheme 58). Me Me Me Me + RS Me Me Me Me + Me RS RSH RS Me Me Me Me Me Me Me Scheme 58. RF = C8F17. R' = Bu. 20°C XCH2CH2SBu X = 1H-Pyrazol-1-yl. nucleophilic addition of methanethiol at the C≡C bond of 2-meth- RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. [156] described radical sulfanylation of 2-[2-(R-carbonyl)vinyl]furans with aliphatic thiols in the presence of tert-butyl peroxide [156]. Thus ionic addition of thiols at the exocyclic C=C bond of 1-vinylpyrazole at 120°C gives a mixture of the corresponding α. such reactions require milder conditions. N2. As a rule. For example. 2-HOC6H4. [165] reported on quantitative trans-addition of 2-sulfanylethanol at the C≡C bond of tertiary β-cyano-α. as in the nucleophilic addition of butane-1-thiol to 3-arylprop-2-yn-1ols [161] (Scheme 65).3-oxathiolane and 1. R CH 2OH + BuSH R = MeOCO.and stereoselective nucleophilic trans-addition was observed in reactions of aliphatic and aromatic thiols with tertiary acetylenic alcohols having an ester [166] or cyano group [167] in the β-position with respect to the hydroxy group (Scheme 68). 75°C R BuS OH + R OH SBu 2-Arylsulfanyl-2-phenylethenylselenonium salts were obtained by treatment of diphenyl(phenylethynyl)selenonium trifluoromethanesulfonate with arenethiols in isopropyl alcohol in the presence of triethylamine [168] (Scheme 69). 25°C HO R R' OH CN HSCH2CH2OH R = 2-MeOC6H4CH2. Scheme 66. Ts CH + MeSH Et3N Ts SMe R = Me. Scheme 69. Scheme 63. 4-MeOC6H4. Quinoline-2-thiol reacts under relatively mild conditions to give a mixture of substituted 1. 4-NCC6H4. 4-O2NC6H4. O CH + MeSH RO SMe Et3N. Scheme 67. The addition of thiols at the triple bond of ethynyl p-tolyl sulfoxide in chloroform in the presence of triethylamine was strictly stereoselective: only the corresponding Z isomers were obtained [162] (Scheme 66). R' = Alk. The product structure depends on the position of the SH group in the quinoline core. Me R + Me OH R'SH R'S Et3N. 43 No. in the two cases. Scheme 65. reflux 4-MeC 6H4 S O SR ArS Ph SePh2 TfO– CH + RSH Ar = Ph. Likewise. Scheme 68. R = Et. Likewise. NaOH. CN. Et2O.and regioisomeric products. the addition occurred exclu- Nucleophilic addition of quinolinethiols at the C≡C bond of tertiary cyanoacetylenic alcohols occurs in a very complex and nonselective fashion [169–171]. MeCN. Ph SePh2 TfO – + ArSH R = Ph. mixtures of Z and E isomers are formed by nucleophilic addition of thiols at the triple bond of ethynyl p-tolyl sulfone [160] (Scheme 64). 3 2007 . Quantitative and completely regio. Ar. the corresponding trans isomers were formed by nucleophilic addition of 2-aminobenzenethiol to 1-benzoyl-2-trimethylsilylacetylene [163] and of imidazole-2-thiol to 3-phenylprop-2-ynenitrile [164]. R' = Me. Et.REACTIONS OF THIOLS 331 oxybenzyl prop-2-ynoate gives a mixture of Z and E isomers of 2-methoxybenzyl 3-methylsulfanylprop-2enoate at a ratio of 1 : 1.β-acetylenic alcohols (Scheme 67). RR' = (CH2)2. EtOH. Ph. Skvortsov et al. 4-MeC6H4. Scheme 64. CHCl3. 4-ClC6H4. O S 4-MeC 6H 4 Et3N. 0°C RO O sively at the sulfur atom. EtOH Me OH Me R Disubstituted acetylenes could give rise to both stereo.5 with an overall yield of 60% [159] (Scheme 63). R CN + R' OH S Et3N.4-oxathiane (overall yield 72%) and quinolin-2-ol (up to 20%) RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. two different products could be obtained. Ph. R 3S LiOH R2 R1 OH CN OH R1 = Me. R2 = Me. quinoline-5-thiol reacted with tertiary cyanoacetylenic alcohols to afford 60% of 3-(quinolin-5-ylsulfanyl)prop-2-enenitrile [169. RS CH + R'S – [RSC=CHSR' Addition of thiols across the C=O bond of carbonyl compounds has been extensively studied. 43 No. Ph. R3 = i-Pr. Scheme 71. these reactions usually occur in the presence of acid catalysts. Scheme 72. Reactions with equimolar amounts of the reactants lead to the formation of α-hydroxy sulfides which can readily be converted into other sulfides. Me CN + RSH Me OH R = Pr. Probably. followed by reduction of α-hydroxy sulfides thus formed (Scheme 75). R3 = quinolin-5-yl. Conjugate addition of thiols and carbon(II) oxide to alkynes in the presence of AIBN gives mixtures of β-alkylsulfanyl-α. [H+] Ph CH + 2 RSH PhC(SR)2Me (Scheme 70). syn-Addition of thiols to acetylenes in the presence of Pd(II) and Rh(IV) complexes was reported to afford mainly the corresponding α-adducts [173]. Scheme 74. the process involves 2 equiv of thiol to give bis-sulfides. Unlike quinoline-2-thiol. 100°C RS CHO + Ph RS Ph R = C6H13. 170] (Scheme 71). Olah et al. Nucleophilic addition of alkanethiols at C≡C bonds of alkylsulfanylacetylenes occurs very readily and quantitatively yields (Z)-1. The ease of the addition was rationalized [151] in terms of stabilization of the intermediate carbanion by d orbitals on the sulfur atom. Bu.332 KOVAL’ Scheme 73. An efficient procedure was developed for the introduction of phenylsulfanylmethylidene and phenyl- RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol.2-bis(alkylsulfanyl)alkenes [172] (Scheme 72). Scheme 75. Depending on the reactant ratio and reaction conditions. R 1 O + R SH R'SH RS=C=CHSR'] RSCH=CHSR' 3 BF3 · Et2O R1 OH R2 SR3 R2 Et3SiH R1 SR3 R 1 2 R = R' = Alk.β-unsaturated aldehydes and the corresponding sulfides [176] (Scheme 74). 80 atm. 177]. R = Ph. C8H17. as well as using radical initiators [176. Electrophilic addition of thiols to triple C≡C bonds is a very rare case. [178] described a one-pot synthesis of sulfides via addition of thiols at the C=O bond of carbonyl compounds. the only example of such reaction was described by Tokmurzin et al. NC LiOH –ROH S Me Me Me Me + CN Me Me RS S Me Me O O OH Radical addition of thiols at C≡C bonds of acetylenic compounds was reported in a few publications. [174] (Scheme 73). Ph CH + RSH + CO R = Quinolin-2-yl. According to the authors. 2 R = H. Thiols reacted with aldehydes in the presence of hydrogen chloride to give directly α-chloro sulfides [179] (Scheme 76). including those having functional substituents. Scheme 70. 3 2007 . t-Bu. The authors presumed formation of radical anions as reactive intermediates. It was presumed [171] that these products result from transformations of primary adducts of quinoline-2-thiol at the triple C≡C bond. R1R2 = (CH2)3. Ph. Et. t-Bu. Sulfanyl radicals were generated by photochemical [151] and thermal methods [175]. R1 CN + R3SH R 2 Benzene. R 1 N N TsOH.8-dien-20yl acetate [181] and progesterone 20.REACTIONS OF THIOLS Scheme 76. 4-MeC6H4. The process is likely to include initial formation of the corresponding dithioacetals. and addition of the second thiol molecule at the double C=C bond (Scheme 81). R3 = Et. 4-MeOC6H4. MeCN. Scheme 77. phenylsulfanylmethyl group was introduced into the 4-position of 3-oxo-13α. Ph. The procedure is based on the reaction of benzenethiol with aldehydes in the presence of proton donors. [RCH(OH)SR'] O O ZnCl2. 55°C O O SPh (Scheme 79). Scheme 80. Scheme 78. and their reduction with PI3 or P2I4 resulted in formation of mixtures of sulfides.α-dichloro sulfides via chlorination of dithioacetals derived from polyfluorinated aliphatic aldehydes (Scheme 78). hydrocarbons. Likewise. Cl2 RFCCl2SR + RCl + HCl + SCl2 The reaction of piperonal with 2 equiv of benzenethiol in acetic acid in the presence of zinc(II) chloride gave the corresponding bis-sulfide. and treatment of the latter with iodine in acetonitrile afforded 3. 43 No. Et. N RCHO + PhSH + N H N CN I2. The use of excess thiol under acidic conditions favors transformation of carbonyl compounds into bissulfides or dithioacetals that are important intermediate products in the synthesis of various sulfur-containing compounds. 60°C CHO + 2 PhSH CH(SPh)2 R = R' = Alk. O O sulfanylmethyl groups into molecules of heterocyclic and natural compounds having labile hydrogen atoms. R2 = Me. A number of thioacetals were synthesized from ketones and thiols.17α-pregna-4. benzene. HCl RCHO + R'SH HCl RCH(Cl)SR' 333 Scheme 79. using benzenethiol and formaldehyde. RC(O)CH2NO2 + 2 EtSH AlCl3 EtS R NO2 SEt EtSH R CH2 EtS EtSH R EtS SEt Me R = Me.20-ethylene acetal [182]. Ph. AcOH. elimination of nitrous acid molecule to give ethyl alkenyl sulfides. CH2Cl2 3 ZnCl2 R1 R2 SR 3 SR 3 R1R2CHSR3 + R1R2C=O + R1R2CH R1 = Ph. H+ RFCHO + 2 RSH RF SR SR The addition of ethanethiol at the carbonyl bond of α-nitro ketones in the presence of aluminum chloride or boron trifluoride–ether complex was accompanied by reductive substitution of the nitro group [186].14β. 3 2007 . Thioacetalization of appropriate aldehyde with ethanethiol in the presence of camphorsulfonic acid was the key stage in the total synthesis of antibiotic Rifamycin W [187] (Scheme 82). and ketones [185] (Scheme 80).4-methylenedioxyphenyl(phenylsulfanyl)acetonitrile [184] In the recent years. thioacetalization of a carbonyl group with thiols has been widely used in syntheses and transformations of various natural compounds. Markovskii et al. R = Ph. reflux N R PhS O + 2 R SH R2 PI3. For instance. Scheme 81. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. [183] developed a procedure for the synthesis of α. benzenethiol reacted with aldehydes in the presence of benzotriazole to produce 1-[α-(phenylsulfanyl)benzyl]-1H-benzotriazole [180] (Scheme 77). Et2O. Ph. indol-3-yl. Pr. Trifluoroacetic acid [191] and boron trifluoride [192] were reported to catalyze thioacetalization of carbohydrates. One step in the multistep synthesis of L-methionine was sulfanylation of the corresponding aldehyde with methanethiol using zinc(II) chloride as catalyst [188] (Scheme 83). oxiranes. Pattenden and Smithies Scheme 88. benzene. O 2 MeSH. 70°C Cl3C NHR S COOH R = PhSO2. Thiols react with nitriles in anhydrous medium in the presence of hydrogen chloride to give imidothioate hydrochlorides [196. Me H Me Me H Concentrated hydrochloric acid was also used as catalyst in the synthesis of 4. Scheme 87. R' = Et. PhCH2. 197] (Scheme 87). O EtO EtO O NHAc CHO Cl2C=CHCl. (CF3)2C=C(Et). It is known that reactions of alkanethiols with isothiocyanates lead to S-alkyl dithiocarbamates [193.4. 4-MeC6H4. C7H15. C6H13. CHO H HO H OH H OH CH2OH + 2 EtSH Concd. as in the reaction of sulfanylacetic acid with N-substituted trichloroacetaldehyde imines [195] (Scheme 86). RO Me Me Me Me KOVAL’ Scheme 85. MeCN RNH S SR' OCH OAc RO 2 EtSH. i-Pr. 194] (Scheme 85). Me R' Addition of thiols at C=N bonds of imines gives α-amino sulfides. Me Me Me SEt EtSH. Scheme 83. PhCH2.3-bis(ethylsulfanyl)-D -lactose diethyl dithioacetal [190]. 43 No. 48 h Me Me Me Me RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol.334 Scheme 82. Studies on thiol addition at C=N bonds of isothiocyanates and Schiff bases and at C≡N bonds of nitriles are relatively few in number. R' = Bu. Thioacetalization of D-xylose with ethanethiol in the presence of concentrated hydrochloric acid was reported in [189] (Scheme 84). 30°C EtS SEt OAc OAc OAc OAc OAc R' Me Me Me R = CH2=CHOCH2CH2. C5H11. ZnCl2 EtO EtO NHAc SMe SMe O R CN + R'SH HCl. 4-MeOC6H4. Scheme 84. Ring Opening by the Action of Thiols Opening of labile three-membered rings in cycloalkanes. 0–20°C R NH2 Cl– SR' R = NCCH2. 3 2007 . R' = COOMe. thiiranes. RN C S + R'SH Et3N. hν. HCl H HO H CH(SEt)2 OH H OH CH2OH 2. Cl3CCH=NR + HSCH 2COOH R = H. Scheme 86.5-di-O-acetyl-2. and aziridines by the action of thiols is widely used for the synthesis of various functionalized sulfides. the reaction is carried out by heating an epoxy derivative with thiol in an anhydrous inert organic solvent (benzene. i-Pr.) [1. etc. tetrahydrofuran. etc. toluene. Me O N O O + R'SH R DMF–K2CO3 –CO2 R'S Me CONHR R = Me. Scheme 91. PhCH2. Ph.REACTIONS OF THIOLS 335 [198] described a radical stereocontrolled cleavage of the cyclopropane ring in a diterpene derivative by the action of ethanethiol under UV irradiation. Voronkov et al. and the products are the corresponding 2-(triisopropylsiloxy)alkane-1-thiols [206]. The five-membered ring in α-methyl-γ-butyrolactone was cleaved by the action of sodium benzenethiolate to obtain sodium 2-methyl-4phenylsulfanylbutanoate [210] (Scheme 92). PhCH2.) [207]. 4-MeC6H4.2. Scheme 90.4-diones. Scheme 89. Scheme 92. CHNHR N Ph O O + R'SH The ring opening in mono. 3 2007 . The thiirane ring in epithiacarane was cleaved by the action of thiols under basic conditions to obtain α-R-sulfanyl thiols [208] (Scheme 90). The reaction of 2-methylpropane-2-thiol with 2. Opening of oxirane ring by the action of thiols underlies a preparative procedure for the synthesis of β-hydroxy sulfides [1] (Scheme 89) which are converted in some cases without isolation into the corresponding β-hydroxy sulfoxides [199]. [212] described reactions of thiols with 3-substituted 6-methyl-2. reflux PhS Me COONa Opening of the five-membered ring in 4-(R-aminomethylidene)-2-phenyl-4.3-dihydro-4H-1. Me Me S Me RSH. Generally. + RSH O RS OH Opening of five.4trimethyl-4H-1.N'-substituted 4-hydroxymethyl-3. [4 + 2]-cycloaddition of two acetylketene molecules gives rise to 3-acetyl-4-hydroxy-6-methyl-2H-pyran which was RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol.3-oxazine-2. Me + PhSNa O O EtOH–THF 24 h.6-dithiaoctane-1.5-dihydrooxazol-5-ones on heating with thiols in the presence of triethylamine followed an analogous pattern [211] (Scheme 93). The authors believe [213] that the process is mediated by acetylketene which reacts with 2-methylpropane-2thiol yielding the corresponding S-ester. 200] or by treating the substrate with alkali metal thiolate in a polar solvent (dimethylformamide. base Me H Me SR Me SH Ph Et3N. MeOCOCH2CH2. etc. R' = Me.3-epoxypropane with thiols in dimethylformamide in the presence of a phase-transfer catalyst were reported to produce 80–90% of bis-sulfides (RSCH2)2CHOH (R = Ph. Microwave-assisted reactions of 1-chloro-2. cleavage of the six-membered ring was accompanied by elimination of carbon dioxide. Kumar et al.3-bis(sulfanyl)propan-1-ol and obtained N. Bu.and disubstituted oxiranes by the action of triisopropylsilanethiol is completely regioselective. Scheme 94. Et. the yield of corresponding sulfide was 75% (Scheme 88). Scheme 93.3-dioxin-4-one involves opening of the six-membered ring to give S-tert-butyl 3-oxobutanethioate as the major product [213] (Scheme 95). EtOH O SR' NH NHR R = Ph. 43 No.) [201–205]. 2 N R + HSCH2CH(SH)CH 2OH RNHCH 2CH 2SCH 2CH(CH2OH)SCH 2CH 2NHR R = PhCH2CH2. [209] studied reactions of N-substituted aziridines with 2.8-diamines (Scheme 91). 4-MeC6H4. and mixtures of the corresponding E/Z-isomeric sulfides were formed (Scheme 94).and six-membered rings in cyclic carbonyl compounds by the action of thiols was reported more rarely. PhH RP[SCH2CH 2C(O)OEt]2 + RP(O)[SCH 2 CH 2C(O)OEt]2 + RP(S)[SCH 2 CH 2C(O)OEt]2 R1 = Alk. Ph. RSX + Cl N RS N NH2 RSNO + NSR + NH2OH OH O R = Alk. Na. Sulfenamides having no substituent on the nitrogen atom were obtained in 70–98% yield by reaction of thiols with hydroxylamine O-sulfonic acid in the presence of KOH [217] (Scheme 98). NaOCl. R 1SNa + R 2R 3NH Oxidant. R3 = Me. and dinitrogen tetraoxide. the authors succeeded in isolating and identifying disulfide PhSCH=C(t-Bu)C(t-Bu)=CHSSPh from the product mixture. 10–20°C ArSNa + NH 3 ArSNH 2 RPCl2 + HSCH 2 CH 2 C(O)OEt Ar = 2. MeO.3-dioxaphospholane with 2.336 Scheme 95. CH2Cl2. 30°C O P O S R R1 = H. R = t-Bu. 3 2007 . 12 h + t-BuSH Me O O KOVAL’ SBu-t A two-step procedure was reported [7] for the synthesis of sulfenamides from thiols. Ar. P-Sulfanylation is generally carried out in anhydrous solvents in the presence of bases (triethylamine. Cl. R2 = C6H13. For example. Scheme 96. R = C17H35C(O)O. The reaction of 2-chloro1. N-SULFANYLATION Sulfanylation of N-halogenated compounds with thiols constitutes a preparative method for the synthesis of sulfenamides. Ht. R R SH O + O P Cl R Et3N.3-bis(stearoyloxy)Scheme 101. Otani et al. etc. p-aminophenol. pyridine. [214] reported on the reaction of 3. SH COOR3 R2 R1 NH2OSO3H R2 R1 SNH2 COOR3 To avoid side processes. the reaction of alkyl(aryl)dichlorophosphines with ethyl 3-sulfanylpropionate was accompanied by oxidation and sulfurization of the sulfanylation products [218] (Scheme 100). In the first step. Et. These reactions are often accompanied by undesirable side processes. Cl. Scheme 98. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. X = H. both substituted and unsubstituted at the nitrogen atom [6] (Scheme 96). O O O Me Me Me 120°C. CHCl3. Scheme 97. Ar. 43 No.6-Cl3C6H2. MeO. RSH + N 2O 4 RSNO + HNO 3 isolated as a by-product. thiols reacted with N2O4 to form sulfenyl nitrites. 0°C R 1SNR 2R 3 Et3N. 4. Scheme 99. R2R3 = CH2CH2OCH2CH2. Various sulfenamides were synthesized by reactions of thiols with ammonia [215] and amines [216] in the presence of oxidants (Scheme 97).S-containing compounds. Scheme 100.). R = Alk. 3. Ar.4-di-tert-butyl-1-(4-tolylsulfonylimino-1λ4-thiophene with sodium benzenethiolate in methanol.4. R3 = H. and reactions of the latter with p-aminophenol gave the corresponding sulfenamides (Scheme 99). P-sulfanylation is performed in an inert atmosphere. P-SULFANYLATION Nucleophilic substitution of chlorine at a phosphorus atom by RS groups is widely used in syntheses of various P. R2 = H. 50 h Ar = Ph. S-SULFANYLATION Replacement of chlorine at the bivalent sulfur atom in sulfenyl chlorides by RS group is widely used for the synthesis of both symmetric and unsymmetric disulfides [222]. 43 No. Me O Ph 5. pyridine. Chlorobis(diisopropylamino)phosphine was treated with p-chlorophenylmethanethiol in anhydrous methylene chloride using sodium hydride as a base [220] (Scheme 102). which was accompanied by intramolecular ring closure to give fused oxathiaphospholidine (Scheme 103). CH2Cl2 NSO2Ar Benzene. Scheme 102. R = 1H-benzimidazol2-yl. HALOGENOLYSIS OF S–H BOND AND FORMATION OF S-NITROSO DERIVATIVES Halogenolysis of the S–H bond in thiols by the action of halogens is a preparative method for the synthesis of sulfenyl halides. and Bunte’s salts [225] were recently involved in reactions with thiols to obtain unsymmetric disulfides. disulfides [223–225]. Relatively recently. Scheme 103.REACTIONS OF THIOLS 337 propane-1-thiol was carried out in anhydrous chloroform in the presence of triethylamine under argon [219] (Scheme 101). 0–20°C Me Me Replacement of chlorine at the SVI atom in sulfonyl chlorides by RS group is not always selective. Scheme 104. 3 2007 . However. as a result. 18–200°C R S N Na SO2Ar + R'SSR Cl R = R' = Ph. CHCl3. The chlorination is performed as a rule in anhydrous inert solvents (CCl4. CH2SH + [(i-Pr)2N]2PCl far treatment of thiols with sulfenyl chlorides in the presence of organic bases. Corey et al. thiosulfonates [226]. For example. a new procedure has been proposed for the preparation of both symmetric and unsymmetric disulfides by reaction of sodium thiolates with N-arylsulfenyl-N. Scheme 106. Medvedeva and Novokshonov [229] described silylation of thiols with hexamethyldisilazane. these procedures are still fairly rarely used. heterocyclic thiols reacted with arenesulfonyl chlorides in acetone in the presence of pyridine to give the corresponding thiosulfonic acid S-esters [227] (Scheme 105). etc.) RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. and the only preparative method for the synthesis of unsymmetric disulfides remains so On the other hand. 20°C ArSO2Cl + RSH ArSO 2SR Cl OH OH Me 110°C. reactions of 4-methylbenzenethiol with arenesulfonyl chlorides in the presence of triethylamine afforded triethylammonium sulfinates [228].N'-bis(arylsulfonyl)arenesulfinimidamides in anhydrous benzene at room temperature [5] (Scheme 104). Apart from sulfenyl chlorides. RSH + (Me 3Si)2NH RSSiMe 3 + Me 3SiNH 2 6. other bivalent sulfur compounds such as sulfenyl thiocyanates [4]. 7]. Me Me SH Me PhPCl2 PhMe. NSO2Ar R S N SR SO2Ar + R'SNa Cl CH2SP[N(Pr-i)2]2 NaH. which is widely used at present [230–232]. the corresponding trimethylsilyl sulfides were obtained (Scheme 106). 4-MeC6H4. Scheme 105. S P Me Me S P Ph Acetone. 4-MeCONHC6H4. 1-acetyl-1H-benzimidazol-2-yl. sulfenamides [6. 4-MeC6H4. [221] described sulfanylation of dichloro(phenyl)phosphine with bicyclic thiol. An example is demethylation of 1-acetoxymethyl-7-methoxy-4-methylindan [243] (Scheme 111).). [239] reported on the transformation of thiols into disulfides through S-nitroso intermediates. reactions of thiols with NCS are not accompanied by chlorination of α-C–H bonds and other functional groups present in the substrate molecule. 4 h + EtSMe N Some S-nitroso compounds were obtained by reaction of thiols with N2O4 in tert-butyl alcohol in the presence of 18-crown-6 [238]. in reactions of thiols with sodium nitrite in tert-butyl alcohol in the presence of oxalic acid at 26–30°C [237] as shown in (Scheme 108). selective demethylation of 1. The first of these implies heating of a mix- Bays et al. The second procedure for dealkylation of alkyl aryl ethers is based on reactions of the latter with thiols in inert organic solvents in the presence of a catalyst (AlCl3. [234] described syntheses of rotenone analogs using a solution of benzenesulfenyl chloride in methylene chloride. 3 2007 .9. 7.10-tetrahydrophenanthridine [241] (Scheme 110).8. 160°C. Two procedures for carrying out this reaction have been developed. Under analogous conditions. Scheme 107. RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. Reaction of thiols with precursors of nitrosyl cation lead to the formation of the corresponding S-nitroso compounds. in this case.338 KOVAL’ in the absence of UV light. OMe PrSNa.2-dithiol in the presence of BF3 · Et2O [245]. BF3 · Et2O. However. For instance. Scheme 109. DMF reflux. DEALKYLATION WITH PARTICIPATION OF THIOLS Thiolysis of C–O bonds by the action of thiols has been widely used to dealkylate alkyl aryl ethers. Following this procedure. The latter were formed. Demir et al. etc. RSH + NaNO 2 H+.g. 43 No. Some oxahydrindene derivatives were subjected to demethoxylation in the presence of boron trifluoride–ether complex [244]. Furuta and Yamamoto failed to demethylate steroid ether using ethanethiol in the presence of AlCl3 or ethane-1. lithium methanethiolate and sodium ethanethiolate were used as dealkylating agents.. The process includes three steps with participation of disulfides as intermediates (Scheme 107). t-BuOH RSN=O R OMe R OMe OH H+ R OMe R = (10Z)-pentadec-10-en-1-yl. a solution of 4-chlorobenzenesulfenyl chloride prepared by chlorination of 4-chlorobenzenethiol with NCS in methylene chloride at 0°C was then used in the synthesis of thioether analogs of ergoline alkaloids [231]. OMe + EtSNa N ONa DMF. Crombie et al. which is very important in syntheses involving natural compounds. etc. which was prepared by treatment of benzenethiol with N-chlorosuccinimide at 0–2°C. N-chlorosuccinimide (NCS) is frequently used as chlorinating agent [233–236]. RSH + Cl2 RSCl + HCl ture of an ether and sodium thiolate in a polar solvent (dimethylformamide.). Scheme 110. After separation of succinimide. 3 h ONa RSH + RSCl RSSR + HCl RSSR + Cl2 2 RSCl In the recent years. Scheme 108. e. An advantage of this reagent is high selectivity.3-dimethoxy-5-[(10Z)-pentadec-10-en-1-yl)benzene was performed [240] (Scheme 109). the resulting sulfenyl chlorides can be brought into further transformations without isolation. dimethyl sulfoxide. [242] utilized the same dealkylation procedure in the synthesis of a structural analog of morphine. sodium ethanethiolate was used to effect demethylation of 2-methoxy7. this dealkylation procedure is not always effective. Me 339 9. Atmospheric oxygen is the most widely used oxidant both in the presence and in the absence of catalysts (Scheme 114). some of these are very important from the practical viewpoint. they include desulfurization of thiols which leads to unsaturated or saturated compounds. These reactions also give saturated products. other oxidants and oxidizing systems are capable of effecting transformation of thiols into disulfides. RS– · · + O–O 2 RS · RS · + · O–O– RSSR Peroxide radical anion thus formed also participates in the oxidation process (Scheme 116). RSH + (EtO)3P hν RH + (EtO)3P=S Desulfurization of thiols can also be effected with the aid of nickel and its compounds in MeOH–THF (3 : 1) [246] or metallic sodium in liquid ammonia [247]. and Fe(III)–NaI catalytic system [259] were also reported. TRANSFORMATIONS OF THIOLS BY THE ACTION OF OXIDANTS Oxidation of thiols with various oxidants gives the corresponding disulfides as primary products. e. however. For example. the latter could then be oxidized to sulfenic. [260] successfully used RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol.. In the recent years. sodium hypochlorite in acetonitrile [250]. REACTIONS OF THIOLS INVOLVING CLEAVAGE OF THE C–S BOND Reactions of this sort are few in number. phosphorus-containing chromium complexes in acetonitrile [253]. Scheme 114. Scheme 116. It is believed that the oxidation process involves formation of sulfanyl radicals via one-electron transfer from thiolate ion to oxygen [151] (Scheme 115). + EtSH OAc Me CH2Cl2. and sulfonic acids. crystalline ammonium peroxosulfate [254]. Oxidations with atmospheric oxygen under microwave irradiation [257]. depending on the conditions. Scheme 115. some less common oxidants and oxidizing systems have been proposed. moist HIO3 [255]. carbon tetrabromide– potassium carbonate [252]. Thermally induced intermolecular condensation of thiols with formation of sulfides is accompanied by cleavage of the C–S bond in one thiol molecule [1]. e. 43 No. 3 2007 .4-triazole-3-thiol with nitric acid [9].. O H N CH2SH OH– H N CH2 O + H 2S Noncatalytic oxidation is usually performed in alcoholic alkalies.g. RSH + · O–O– RS · + HOO– RSH + HOO – RSH + · OH RS · + OH – + HO · H 2O RS · + Reactions of alkanethiols with triethyl phosphite under UV irradiation give saturated hydrocarbons [9] (Scheme 113). for purification of oil from sulfur compounds. calcium hypochlorite in the presence of montmorillonite [251]. Apart from atmospheric oxygen. Scheme 113.g. AlCl3 OMe + EtSMe OAc OH 2 RSH + 1/2 O 2 RSSR + H2O 8. depending on the oxidant nature and reaction conditions. Otaka et al. First of all.4-Triazole was obtained by oxidative desulfurization of 1. hydrotalcite clay [258]. treatment of cysteine-containing proteins with alkali results in elimination of the thiol groups from the cysteine fragments which are thus converted into dehydroalanine moieties [9] (Scheme 112). sulfinic.2.2. and vanadium oxide in combination with tert-butyl hydroperoxide [256]. silica-supported peroxosulfuric acid [249]. the relevant data reported till 1997 inclusively were covered by review [248]. Scheme 112.REACTIONS OF THIOLS Scheme 111. 1. A.. 232. While determining primary structure of cysteinecontaining proteins. B. B. B.. I. Baba. S=N.. 1993. K. Eds.. T. 9... S. 1405.. R. O’Brien.. 396. and Voith.. Sundara. Versatile reactivity of thiols originates primarily from their specific structure. p. Therefore. 168. Synth. Chem. 8175. Indian J. Wuts.. Kidwai.. 2000. Chakraborti. reductive cleavage of disulfide bridges is often necessary.. 1994. oxidative imination with N-halogen and N. J. Gu. N.V. Usp. and Sahoo. A. 63.. S–N. 145. 1239. vol.. Novozhilov. D. Obrecht.. K. p.A. Indian J. S.. 3693. 23.. M.. 9155.M. 12. J. 24. Res.. Chertkov. 43 No. W. 1999. N. 5. K. Koval’. Sect. therefore. S–P. p. Org.C. vol. R. Koval’.P. 55. Towers. 60. 1313.V. Nakajo. Wendeborn. 10. J.. Mel’nikov.M. p. 263. Dave. 38.H. 41. Koval’. 338.. Ser. 1996. M. 1998. K. 1993. Khim. 14.. These reactions have been described in detail in recent reviews [263–266]. Chem. 673. H.. 35. and Thomas. T.V.. 7. D. I.. Moscow: Khimiya. D. Oxford: Pergamon. Khim. vol. p. Org. Arkhipov. 4. 69. 36. Vestn. p. and Chuchilowsky. vol. R. namely from the presence of a highly reactive center. 1992. e. Chem. Russ. 1998. Sect. Kimura... an example is reductive deiodination of 21-iodocorticosteroids [261]. 31. 21.. and Bhaduri. vol.S. 1998. K..V. Synlett.. 1979.V. 5. 65. depending on the conditions. 16. Sucholeiki. Commun. 1996. I.L. Khimicheskie sredstva zashchity rastenii (Chemical Means for Plant Protection)... N. p. vol. Imtiaz. 13. 1992. Soto. and high lability of the S–H bond which is capable of undergoing heterolytic or homolytic dissociation to give such reactive intermediates as sulfanyl radicals and S-centered cations or anions. Undavia. p.. vol. 121.D. Sci. 1992. 2001. Translated under the title Obshchaya organicheskaya khimiya. pp. J. Tetrahedron Lett. Ohyama. Litvinov. and Ollis. S.. I. vol..V. A. Jill.340 KOVAL’ Ti(OCOCF3)2 to build up S–S bonds in the synthesis of cysteine-containing peptides. 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