Sulfenylating agents

Second, in comparing either the behavior of [65] vs. [67], or that of [66] vs. [68], one sees that the rate of intramolecular displacement of CN- from —SCN by —S02 is about 30 times faster than the rate of intramolecular displacement of SO, from —SSOj by —SOj. This is striking because it contradicts the belief sometimes expressed in the literature, but not apparently founded on any real experimental data, that Bunte salts are considerably more reactive as sulfenylating agents than thiocyanates. The data in (178)—(181) clearly indicate that a thiocyanate can be more reactive than a Bunte salt as a sulfenylating agent. 

Modification of Tryptophan Residues. Tryptophan residue also could be determined quantitatively by a modification with a sulfenylating agent such as 2-nitrophenyl sulfenyl chloride in 30% acetic acid ( ). Since both oxidized and sulfenylated tryptophan gave characteristic absorption at 365 nm, the extent of tryptophan modification was calculated from the mean difference between the sulfenylated protein and the kynurenine. The absorption contributed by kynurenine was comparatively weak. 

Compound 35, along with some other structurally related sulfenylating agents, has also been found to be useful for the functionalization of 1,3-dicarbonyl compounds 38 (Eq. 9). Lactones and / -dicarbonyl compounds were a-sulfenylated in the presence of (DHQD)2PYR in high yields and moderate to good enantioselec-tivities (51-91% ee) [34]. 

All acetylenes with a terminal triple bond are instantaneously converted into the alkali acetyiides by alkali amides in liquid ammonia. For many alkylations with primary alkyl halides liquid ammonia is the solvent of choice and the functionalization with oxirane can also be carried out in it with good results. Reactions of RC=CM with sulfenylating agents (R SSR R SC=N, R SSC R ) or elemental sulfur, selenium or tellurium are mostly very successful in ammonia, the same holds for the preparation of RCsCI from RGCM and iodine. The results of couplings with carbonyl compounds are very variable. 

The concept of stereocontrol by the ion pan mechanism in the electrophilic additions of sulfenyl chlorides has been further discussed - by Zeflrov, using norbornadiene (49) as a substrate. The addition of sulfenyl chlorides to 49 has been reported to give a product distribution markedly dependent on the sulfenylating agent. In particular, it has been observed s addition of p-toluenesulfenyl chloride gives only the anti 1,2-... 

Entry 4 is a special type of sulfenylation agent. The sulfoxide fragments after O-acylation, generating a sulfenyl electrophile. 

Functionalization of multiple bonds. The sulfenylating agent attacks alkenes and alkynes thus in the presence of hydrobromic acid it results in bromosulfenyla-... 

In some cases this further reaction can be suppressed by adding the sulfenylating agent (preferably in excess) in one portion, but a more successful procedure involves addition of RR CHM to a solution of a (100%) excess of R"SSR". If the disulfide is non-volatile (PhSSPh ) and hence the excess is difficult to remove from the product mixture, this procedure is not attractive. Especially in the cases of metallated nitriles RCH2C=N and ketone enolates the further sulfenylation is a problem which has not yet been satisfactorily solved. 

Heterofunctionalisation of carbonyl compounds in the a-position has become an important facet of oiganocatalytic enamine-mediated reactions. In 2005, the Jorgensen group described asymmetric a-sulfenylation of aliphatic aldehydes using TMS-protected prolinol catalysts. The best sulfenylating agent was M-benzylsulfanyl-1,2,4-triazole. Other catalysts, such as proline, prolinol, prolinamide or other secondary amide were less effective. The catalyst with bulkier aromatic groups (C2a) afforded the most enantioselective reaction (Scheme 8.39). 

Heterosubstituted sulfides are excellent sulfenylating agents for soft bases owing to the fact that most of the hetero atoms (e.g., O, N) are hard which favors both the dissolution of the soft-hard combination and the formation of new soft-soft bonds. Thus, the N-8 reagents (97-101) are particularly popular for transfer of the thio function. 

Sodium cyanide N (Arylthio)isatins as sulfenylating agents... 

Alkyl and aryl pyridyl disulfide-W oxides are also effective sulfenylating agents. Thus, treatment under prolonged reaction time of 2,2 -dipyridyl disulfide-)V,) -dioxide with 2 equiv of thiol generates s)mimetrical disulfides and 7V hydroxy-2-thiopyridone as shown in eq 3. ... 

More conveniently, 2-(methylthio)alkanoic esters are prepared from 2-acetylalkanoates (eq 2)] MeSSMe cannot replace MeSS02Me as the sulfenylating agent in this transformation. Advantages of these methods over others such as sulfenylation of an alkanoic acid and its ester or alkylation of (methylthio)acetic acid are (1) simplicity of the procedure (2) efficiency and convenience of using inexpensive base (EtONa) and EtOH as solvent with high product yields and (3) no bissulfenylation. Moreover, the latter... 

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