Sulfenic acid derivatives

The intermediate sulfenic acid derived from a penicillin sulfoxide has been trapped by a large assortment of reagents and, in one case, the sulfenic acid itself has been isolated (74JA1609). Only some of these products will be discussed here, and the reader is referred to the cited reviews (especially B-80MI51102) for additional examples. 

The attack by the thiolate anion on the N-oxide oxygen of 62 produces the intermediate sulfenic acid derivative 65, which, in the presence of thiols, further reacts with the thiolate anion, to give the oxime 66, which has been isolated among the reaction products. By contrast, spontaneous loss of the halide anion from 65 affords the ni-troso intermediate 67 that, by losing NO and the thiyl radical directly, or through 68, produces the a-nitrosoolefm 69. By a Michael type reaction with water this last product immediately yields the final oxime 70, which has been isolated among the reaction products. 

Sulfenic acid derivatives (RSX) such as esters, amides and halides are reactive owing to the relative weakness of the S-X bond, and they consequently react with nucleophilic reagents (Nu-) (Scheme 33). In such nucleophilic substitutions at the sulfenyl sulfur atom, the reaction mechanism may be SN1 (Scheme 34). 

Topics which have formed the subjects of reviews this year include excited state chemistry within zeolites, photoredox reactions in organic synthesis, selectivity control in one-electron reduction, the photochemistry of fullerenes, photochemical P-450 oxygenation of cyclohexene with water sensitized by dihydroxy-coordinated (tetraphenylporphyrinato)antimony(V) hexafluorophosphate, bio-mimetic radical polycyclisations of isoprenoid polyalkenes initiated by photo-induced electron transfer, photoinduced electron transfer involving C o/CjoJ comparisons between the photoinduced electron transfer reactions of 50 and aromatic carbonyl compounds, recent advances in the chemistry of pyrrolidino-fullerenes, ° photoinduced electron transfer in donor-linked fullerenes," supra-molecular model systems,and within dendrimer architecture,photoinduced electron transfer reactions of homoquinones, amines, and azo compounds, photoinduced reactions of five-membered monoheterocyclic compounds of the indigo group, photochemical and polymerisation reactions in solid Qo, photo- and redox-active [2]rotaxanes and [2]catenanes, ° reactions of sulfides and sulfenic acid derivatives with 02( Ag), photoprocesses of sulfoxides and related compounds, semiconductor photocatalysts,chemical fixation and photoreduction of carbon dioxide by metal phthalocyanines, and multiporphyrins as photosynthetic models. 

The biochemistry of onion flavor is now well known and has been extensively reviewed by Shankaranarayana et al. [67]. The chemistry involved has been covered in detail in an earlier chapter of this text. The distinctive flavor of onion and other alliaceous vegetables is due to S-alk(en)yl derivatives of L-cysteine sulfoxide, which are rapidly hydrolyzed by the enzyme alliinase to give an unstable sulfenic acid derivative together with pyruvic acid and ammonia. The sulfenic acid compound breaks down and rearranges to form the relatively more stable thiopropanal S-oxide, which has lachrymatory properties, or it reacts with other compounds to produce a complex mixture of di- or trisulfides which ultimately characterize the product. 

Other azetidinone derivatives useful for the synthesis of new p-lactam structures have been prepared by variations in the reaction of a trialkyl-phosphite with the sulfenic acid derived from a penicillin sulfoxide. 

The (E)-(prop-l-en-l-yl)sulfenic acid derived from the related amino acid occurring in onion and known as isoaUiin behaves differently. It isomerises on catalysis with enzyme LF-lyase... 

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