Theoretical study of a termolecular mechanism for the reaction of (trimethylsilyl)thiazole with carbonyl compounds

The mechanism of the addition of 2-silylthiazole to formaldehyde has been studied by ab initio calculations at the MP2/6-31+G*//6-31G* level. The reaction is predicted to occur by the concerted formation of an N-[(silyloxy)methyl]thiazolium-2-ylide intermediate followed by nucleophilic addition of the intermediate to another formaldehyde molecule. Loss of the first formaldehyde gives the addition product. An alternative mechanism involving 1,2-migration of the ylide to form 2-[(silyloxy)-methyl]thiazole is prevented because of the high activation energy of the 1,2-shift. A third mechanistic alternative involving the formation of an N-silylthiazolium-2-ylide through 1,2-silyl migration is also discounted due to a high activation energy.