A Mechanistic Study of the Wittig Reaction Between a Cyclic Anhydride and a Stabilized Phosphorane

Abstract

The structure of an isolated acyclic intermediate in the Wittig reaction between succinic anhydride and ethoxycarbonylmethylenetriphenylphosphorane has been shown by X-ray structure analysis and DEPT n.m.r .to be the phosphorane (4a) rather than the alternative phosphonium salt (4b). However, an intermediate was not observed in the Wittig reaction between the phosphorane (1b) and cyclic anhydrides. Both the stabilized phosphoranes (1a,b) react with succinic, phthalic and glutaric anhydrides stereoselectively to produce E enol lactones. Some mechanistic aspects are discussed. The assignment of the enol lactone stereochemistry was achieved by n.O.e. difference n.m.r. methods.