PREPARATION OF ESSENTIALLY ISOMERICALLY PURE METHYL E-2-(2-ARYLOXYMETHYLENE-PHENYL) CROTONATES, AND INTERMEDIATES THEREFOR

摘要

A process for preparing substantially isomer-pure E-2-(2-aryloxymethylene phenyl)-crotonic acid methyl esters having formula (Ia), in which R stands for an aromatic residue substitued by the usual groups and R' stands for a C1-C3 alkyl group, is characterised in that a corresponding 2-(2-aryloxymethylene phenyl)-.alpha.-keto-acetic acid methyl ester having formula (II) with an alkyl metal compound having formula (III), in which M stands for a metal ion equivalent, first yields the corresponding 2-(2-aryloxymethylene phenyl).alpha.-hydroxybutyric acid methyl ester having formula (IV), which is then dehydrated in the presence of an acid into a mixture of E- et Z-2-(2-aryloxymethylene phenyl)-crotonic acid methyl esters having formulas (Ia) and (Ib). This mixture is finally converted into the substantially isomer-pure E-2- (2-aryloxymethylene phenyl)-crotonic acid methyl ester (Ia) in the presence of a base in an inert polar solvent.