Alkaloid formation through N-oxide intermediates; regioselective synthesis of (±)-corytuberine by redox reaction

Abstract

Reaction of (±)-reticuline N-oxide (1) with cuprous chloride in methanol followed by treatment with sodium hydrosulphite gave the aorphine alkaloid, (±)-corytuberine (8) in good yield. Protoberberine alkaloids, (±)coreximine (4) and (±)-scoulerine (5), were obtained by reaction of the N-oxide (1) with ferrous sulphate in methanol. On the other hand, formation of the phenol oxidative coupling product, (±)-orientalinone (9), from (±)-orientaline N-oxide (2) with cuprous chloride was less effective and formation of the protoberberine (7) from the N-oxide (2) with ferrous sulphate required acidic conditions.