Synthesis of 3-bromo-2-pyrones and their reactions with bases

Abstract

The synthesis of α-pyrones related to isodehydracetic acid (2,4-dimethyl-6-oxopyran-3-carboxylic acid), their bromination, and the reaction of the bromo-compounds with bases have been reinvestigated and extended. The sodium-catalysed condensation of β-keto-esters and related compounds with acetyenic esters provides a satisfactory general method for synthesis of the α-pyrones. The reactions of the bromo-pyrones with alkali depend markedly on the structure of the pyrone, the nature of the alkali, and the reaction conditions, and give, variously, acyclic, cyclopropane, cyclopentane, and furan acids or their decarboxylation products. The formation of alkylidenecyclopropanes like Feist's acid is not a very general reaction.