Comparative intramolecular dehydrative lactonization of 4-oxocarboxylic acids

Abstract

Reaction of 3-(p-toluoyl)propanoic acid, 1a (R = H) with refluxing acetic anhydride resulted quantitatively in 2, a β,γ-unsaturated γ-lactone, which was then converted into 3a, an α,β-unsaturated lactone by isomerization with triethylamine. The methyl-substituted compound 1b (R = Me), an analogue of 1a, afforded the 2(5H)-furanone 3b directly by heating with Ac 2 O. Similar reaction of the cycloalkane-containing oxocarboxylic acids (4,5) led in excellent yields to the fused furanones 6 and 7, while treatment of 2-formyl-, 2-acetyl-and 2-(p-toluoyl)benzoic acids (8a-c) with Ac 2 O gave the 3-acetoxy-1-(3H)-isobenzofuranones, 9a-c.