Stable Cyclic Peterson Olefination Intermediates.

Carbonyl olefination reactions have become essential to organic chemistry since Wittig's report on the first reaction of this kind using a phosphorus ylide. While the reaction mechanism of the Wittig olefination is well understood the same cannot be said about the related silicon analogue, the Peterson olefination. Both an open chain, betaine like intermediate and a cyclic 1,2-oxasiletanide intermediate have been discussed since Peterson's original publication, with little evidence for the cyclic intermediates. Herein we present the synthesis and characterization of several stable cyclic Peterson olefination intermediates synthesized via the reaction of an α-silyl carbanion with various ketones. The α-silyl carbanion is stabilized by three pentafluoroethyl groups at the silicon atom. Furthermore, it bears a carbanion stabilizing phenyl group α to the carbanion.