The Birch Reduction of Heterocyclic Carboxylic Acids. I. The Birch Reduction of 3-Furoic Acid

The reduction of 3-furoic acid with sodium and 2-propanol in liquid ammonia gave 2,3-dihydro-3-furoic acid, which was isolated as a methyl ester (1) in 85% yield. The acid-catalyzed addition of methanol, ethanol, or 2-propanol to the ester 1 yielded 5-alkoxytetrahydro-3-furoate ester, 2, 3, or 4, respectively, in a quantitative yield. When methanol or ethanol was used as a proton source in the reduction, work-up of the reaction mixture gave 5-alkoxytetrahydro-3-furoic acid, which was isolated as the methyl ester, 2 or 3, in 87 or 92% yield, respectively. A mechanism for the Birch reduction of aromatic carboxylic acids is proposed.