Photochemical reactions of N-phenylacetyl and N-(2-iodophenylacetyl) derivatives of 1,2,3,3a,4,5-hexahydroindol-6-one

Abstract

Irradiation of 1,2,3,3a,4,5-hexahydro-N-(2-iodo-4,5-dimethoxyphenylacetyl)indol-6-one (2) gave 3,3a,4,5-tetrahydro-10,11-dimethoxyindolo[7,1-ab][3]benzazepine-1,7(2H,8H)-dione (3) and the deiodination product (4). The latter (4) then underwent a photo-Fries rearrangement to 1,2,3,3a,4,5-hexahydro-7-(3,4-dimethoxy-phenylacetyl)indol-6-one (5), which, upon further irradiation, gave 3,3′,4,4′-tetramethoxybibenzyl (13), 2,3,3a,4,-5,6-hexahydro-6-oxo-1H-indole-7-carbaldehyde (12), and -7-carboxylic acid (14). The production of compounds (12)–(14) is accounted for by a mechanism involving a type I cleavage and subsequent keten formation. The presence of a keten intermediate was demonstrated by nucleophilic addition of water, an alcohol, or an amine.