Horner-Wadsworth-Emmons Modification for Ramirez gem-Dibromoolefination of Aldehydes and Ketones Using P(Oi-Pr)3

A simple procedure for the use of triisopropylphosphite in the Ramirez olefination is described. This reagent is equally or more reactive than PPh 3 toward aldehydes and ketones in the GEM-dibromoolefination of aldehydes and ketones. Under the reaction conditions, an α-bromoketone gave a novel tribromomethyl-substituted oxirane product in good yield. The substrate-dependent nature of this reaction suggests that this Horner-Wadsworth-Emmons equivalent of the Ramirez GEM-dibromoolefination reaction proceeds through an ionic mechanism.