Synthesis of (trimethylsilyl)thiazoles and reactions with carbonyl compounds. Selectivity aspects and synthetic utility

Synthetic routes to all possible regioisomeric mono- and bis(trimethylsilyl)thiazoles as well as to the tris-(trimethylsilyl) derivative via lithiation-silylation sequences of the thiazole ring followed by selective protodesilylation in some cases are described. (Trimethylsilyl)thiazoles serve as thiazolyl donor synthons upon reaction with carbonyl compounds (ketenes, acyl chlorides, aldehydes) for the preparation of mono- and bis-substituted thiazoles in very good yields. Carbodesilylation occurs more readily at the 2- than the 5-position, whereas no reaction takes place at the 4-position. A mechanism via a thiazolium 2-ylide as an intermediate is suggested for the carbodesilylation at the 2-position.