An investigation of the Wittig reaction between a series of monosubstituted phthalic anhydrides and ethoxycarbonylmethylidenetriphenylphosphorane

Abstract

The title reaction has been investigated using a range of phthalic anhydrides substituted at the 3- or 4-positions with electronically dissimilar functional groups. The structures of the 3-ethoxycarbonylmethylidenephthalides formed in these reactions have been determined by both chemical and spectroscopic means. The regioselectivity of attack by the phosphorane on an unsymmetrical phthalic anhydride appears to be largely dependent upon the electronic effects of the substituent which render one of the anhydride carbonyls relatively more or less susceptible to nucleophilic attack. In general, (E)-ylidenephthalides are formed predominantly.