Electrolytic decarboxylation reactions. I. Electrosyntheses of γ-substituted butyrolactones and γ-substituted α,β-butenolides from γ-substituted paraconic acids

The product-selective electrolytic decarboxylation of γ-substituted paraconic acids has been studied (1) in dry methanol using sodium methoxide by addition of iron powder or ferric nitrate on platinum electrodes, (2) in dry methanol using sodium methoxide on carbon rod electrodes, and (3) in a mixed solvent of triethylamine-pyridine-water on carbon rod electrodes. Conditions 1 and 2 resulted in exclusive formation of 7-substituted butyrolactones in 80-99% yields, whereas condition 3 provided α,β-unsaturated butenolides in 70-90% yields. By means of the butenolide synthesis dl-3-carboxy-8-hydroxy-Δ³-menthene 7-lactone, a key intermediate for the preparation of dl-menthone, could be prepared.