Thiosulfinates, racemization

Much attention has been devoted to the acid- and nucleophile-catalyzed racemization of thiosulfinates. As a result of the extensive studies by Kice and his co-workers (112) and by Fava (281), it is clear now that the easy racemization of thiosulfinates caused by acids and bases (e.g., pyridine) is related to the scission of the sulfur-sulfur bond and the formation of sulfenic acid or its anion as an achiral intermediate. As expected, introduction of steric hindrance... 

Another class of sulfoxidic substances, the aryl thiosulfinates ArS(0)SAr, which have recently been prepared in an optically active form, exhibit exceptionally high optical lability Racemization of thiolsulfinates may occur in an uncatalysed path involving pyramidal inversion at the sulfoxide sulfur. Reaction rate coeffi-... 

We have used chiral y-cyclodextrin GC columns under isothermal GC-MS conditions (column temperature 9 120 ) and found that enantiomers of /ran -zwiebelane (9a, Figure 2) and the thiosulfinates MeS(0)SMe, MeS(0)SPr-/i, and MeSS(0)Pr-/i (Figure 3) can be resolved and that individual enantiomers are stable under the analytical conditions (25). However, analysis of an onion extract on the chiral column showed that all of these con unds were present as racemic mixtures, su esting that asymmetric induction is not involved in their formation from achiral sulfenic acid ... 

Proteus mirabHis and Proteus vu aris reduced the same sulfoxide with opposite enantioselectivity [121]. The resolution of racemic aDcylaryl sulfoxides and thiosulfi-nates by dimethyl sulfoxide reductase from the anaerobic bacterium Citrobacterbmaldi gave the corresponding enantiopure alkylaryl sulfoxides and thiosulfinates [122]. 

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