Furan Derivatives. V. The Syntheses of 4,5-Dihydro-3H-naphtho[1,8-bc]furans Using Strong Bases

The reaction of ethyl (4-methoxy-8-oxo-5,6,7,8-tetrahydro-1-naphthyloxy)acetate and potassium hydroxide gave a mixture of 6-methoxy-4,5-dihydro-3H-naphtho[1,8-bc]furan and 6-methoxy-4,5-dihydro-3H-naphtho[1,8-bc]furan-2-carboxylic acid in total yield above 90%. The mechanisms of formation of two products were examined, and potassium 2a-hydroxy-6-methoxy-2a,3,4,5-tetrahydro-2H-naphtho[1,8-bc]furan-2-carboxylate was isolated as a precursor of 6-methoxy-4,5-dihydro-3H-naphtho[1,8-bc]furan. It has become apparent that strong bases such as sodium hydroxide, sodium ethoxide, and sodium hydride were also useful for syntheses of 6-methoxy-4,5-dihydro-3H-naphtho[1,8-bc]furan derivatives.