α-Pyrones. II. The Synthesis of α-Pyrones From α,β-Unsaturated Aldehydes. Part II

Abstract

It is shown that the reaction of acrolein with bromomalonate in the presence of an alkali alkoxide, leading to a 2-formylcyclopropane-1,1-dicarboxylate, may be applied to the steroid series; thus, a 20-methylene 21-aldehyde gives in excellent yield the corresponding cyclopropane derivative. The possibility of converting such systems to α-pyrones was investigated in the case of the acrolein adduct, diethyl 2-formylcyclopropane-1,1-dicarboxylate. While its cyclopropane ring could not be isomerized to an olefin with aluminum chloride or by reactions catalyzed by transition metals and while photolysis led to a dihydrofuran derivative, pyrolysis in high vacuum at 550–575° afforded directly an α-pyrone, ethyl coumalate. Evidence is put forward for the intermediacy of 3-ethoxycarbonyl-α-pyrone in this reaction.