The photochemistry of papaverine N-oxide

Abstract

Ultraviolet irradiation of papaverine N-oxide (2) in methanol gave papaverine (1) and 6,7-dimethoxy-2-(3',4'-dimethoxybenzyl)isocarbostyril (3). Irradiation of (2) in acetone resulted in the isolation of 7,8-dimethoxy-2-(3',4'-dimethoxybenzyl)-l,3-benz- oxazepine (4) by crystallization of the photolysate, and of 5,6-dimethoxy-2-(3',4'-di- methoxybenzy1)benzofuran-3-carboxaldehyde (6), 5,6-dimethoxybenzofuran-3-yl- 3',4'-dimethoxybenzyl ketone (7), 5,6-dimethoxy-2-(3',4'-dimethoxybenzyl)benzofuran (8), and papaverine by preparative thin-layer chromatography on silica gel. Evidence is presented in support of the formation of (6) and (7) from the valence tautomer (5) of the oxazepine (4), by acid-catalysed hydrolysis and rearrangement.