Photochemical reduction of 1,2-naphthoquinones with xanthen. Investigation by means of a photo-CIDNP technique

Abstract

Photochemical reactions of 1,2-naphthoquinone and its derivatives with xanthen, a hydrogen donor, have been investigated. 1,2-Naphthoquinones, in general, produced the stable adducts (2), 9,9′-bixanthenyl, and xanthone together with a small amount of quinhydrones. 4-Substituted 1,2-naphthoquinones, however, gave the corresponding naphthalene-1,2-diols as the major products. Investigation by means of a CIDNP technique indicated the formation of unstable products, judging from the strongly polarized ¹H n.m.r. signals, though the unstable intermediates did not accumulate in the reacting solution. Adducts (2), naphthalene-1,2-diols, and 1,2-naphthoquinones themselves also showed polarized ¹H n.m.r. signals. From these results, the reaction mechanism was deduced.