An epoxide intermediate in nucleophilic acylations by thiazolium precursors.

Computational work at the MP2/6-31+G(d,p) level is used to explore the nucleophilic species derived from the fluoride activation of O-silylated thiazolium carbinols. These species recently have been shown by Scheidt to be useful acyl anion synthons, but the mechanism of their formation has been an open question. The data point to an unusual spiroepoxide intermediate that rearranges via acid/base chemistry to give the active nucleophile. The addition of the nucleophile to nitroethene is also examined.