Synthesis of 4-ylidenebutenolides. A practical route to 2-en-4-ynoic acid intermediates based on conjugate addition of alkynyl-lithium reagents

Abstract

Conjugate addition of alkynyl-lithium reagents to diethyl ethoxymethylenemalonate, followed by simultaneous saponification and 1,2-elimination of ethanol from the intermediate adducts, viz(18), in the presence of ethanolic potassium hydroxide, provides a useful synthesis of substituted propargylidenemalonic acids (19). Cyclisation of the propargylidenemalonic acids, using known procedures then leads to the corresponding 4-ylidenebutenolides, e.g.(20) and (21)