The Synthesis of 5-Oxo-2,5-dihydrofuran-2-ylideneacetic Acids

Abstract

The 5-oxo-2,5-dihydrofuran-2-ylideneacetic acids (2a), (3a), (9a), (10a), (11a), (12a) and (13a) have been synthesized by a procedure which allows the unambiguous assignment of the stereochemistry about the double bond in each isomer. The method, of general application, enables the acids to be prepared from the corresponding t-butyl esters with acid without isomerization about the double bond. The t-butyl esters are available from the Wittig reaction between anhydrides and t- butoxy-carbonylmethylenetriphenylphosphorane.Where mainly one isomer is produced in the Wittig reaction, isomerization to an easily separable mixture of the esters can be achieved. Aspects of the isomerization of enol-lactone esters (e.g. (2b)) are described.