Selective synthesis of enethiols

It must be noted that this selective synthesis of enethiols from thioketones is restricted to cases for which regio- and stereoselective deprotonation occurs, as was achieved above with the symmetrical thiones (2a)-(2d). 

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Enethiols 61 are tautomerically stable isomers of thioketones 60 and, in contrast to enols, enethiols have been isolated and characterized. This method provides a route for the selective synthesis of enethiols by deprotonation of 60 and quenching with trimethylchlorosilane, since under these conditions no isomerization takes place. 

This study was complemented by a selective synthesis of the tautomeric enethiols [77]. Aliphatic thioketones were deprotonated by LDA, silylated, and the resulting silyl vinyl sulfides were smoothly converted to enethiols by simple addition of methanol. These are stable compounds which do not equilibrate with thioketones, this behaviour probably related to the extremely mild conditions of the (easy) cleavage of the silicon-sulfur bond. 

It is interesting to note that nonsilylated enethiols have only been prepared as mixtures with their isomeric thioketones.4a,c The first selective synthesis of aliphatic enethiols was performed by Metzner52 by deprotonation of enethiolizable thioke-tones 42 with LDA and reaction of the enethiolates with trimethylsilylchloride. The subsequent methanolysis of silyl vinyl sulfides 43 afforded enethiols devoid of isomeric thioketones. Treatment of the enethiolates with various proton sources afforded instead mixtures of thioketones and enethiols (Scheme 31). 

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