Ketene S,N acetals from thioamides

In addition to its basicity, the structural nature of the base can affect the course of the reaction. For example, a sterically imposing base such as diisopropylethylamine was prevented from abstracting proton (Ha) residing in a congested environment of the a-thioiminium salt (23 Scheme 6) Instead, a less-hindered hydrogen (Hb) was abstracted, leading to formation of a proposed S,N-ketene acetal (24), which underwent rearrangement to yield the a-alkylated thioamide (25) as the major product. A less... 

The efFicienqr of sulfoxides as chiral inductors for the thio-Claisen rearrangement has been demonstrated with N,S-ketene acetals derived from racemic 2-sulfinyl dithioacetates [72], Moreover, these reactions were successfully extended to the enantiopure series using chiral thioamides as substrates [125]. The source of chirality is the easily available and cheap D-glucose [126]. Remarkably, both enantiomers of the starting 2-sulfinyl thioacetamides can be selectively obtained from the same D-glucose. 

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