A SIMPLIFIED PROCEDURE FOR THE STEREOSPECIFIC TRANSFORMATION OF 1,2-DIOLS INTO EPOXIDES

A simple, 'one-pot' procedure for the conversion of vicinal diols into epoxides via halohydrin ester intermediates has been developed. This method tolerates a wide range of functionality including acid sensitive functional. The transformation proceeds via a, usually highly regioselective, nucleophilic opening of a cyclic acetoxonium intermediate, generated from a cyclic orthoacetate and Me3SiCl, acetyl bromide or acetyl chloride/NaI to form 1-acetoxy-2-chloride, 1-acetoxy-2-bromide or 1-acetoxy-2-iodide intermediates, respectively. No epimerization occurs, even with benzylic substrates. Subsequent base mediated methanolysis furnishes epoxides in excellent overall yield. Application of this method led to an efficient formal synthesis of the leukotriene antagonist SKF 104353, commencing with the highly enantioselective cis-dihydroxylation of methyl 3-[2-(8-phenyloctyl)phenyl]propenoate.