The Chemistry of Phthalide-3-carboxylic Acid. III. Decarboxylation of Salts in the Presence of α,Β-Unsaturated Ketones

Abstract

Potassium phthalide-3-carboxylate (3-oxo-1,3-dihydroisobenzofuran-1- carboxylate ) decarboxylates readily in dimethyl sulfoxide at 145°, and the intermediate phthalidyl anion is efficiently trapped by α,β - unsaturated ketones. The major 1,4-addition product is accompanied by smaller amounts of an isomeric product formed by subsequent cyclization and rearrangement, and sometimes traces of a 1 : 2 1,4-addition product. The caesium salt gives slightly more cyclized product, and the lithium salt undergoes very slow decarboxylation. The synthetic usefulness of the salt decarboxylation is compared with that of the free acid.