Improved E-selectivity in the Wittig reaction of stabilized ylides with alpha-alkoxyaldehydes and sugar lactols.

[reaction: see text]. The Wittig reactions of alpha-alkoxyaldehydes and sugar lactols with stabilized ylides such as (alkoxycarbonylmethylene)triphenylphosphoranes typically proceed with low E-selectivities. However, we have discovered that the reaction of such aldehydes with (methoxycarbonylmethylene)tributylphosphorane in toluene in the presence of catalytic amounts of benzoic acid proceeds to give the E-alpha,beta-unsaturated esters with high selectivities and in high yields.