Synthesis of 3,4-bridged indoles by photocyclisation reactions. Part 1. Photocyclisation of halogenoacetyl tryptophan derivatives

Although irradiation of N-chloroacetyltryptophan results in a poor yield of photocyclisation to the indole 4-position due to competing cyclisation to C-2, the photocyclisation of (dichloroacetyl)tryptophan derivatives gives, after addition of a nucleophile in work-up, 7-substituted pyrrolobenzazocines in good yield and with trans-stereospecificity. N-(Trichloroacetyl)tryptophan derivatives also undergo photocyclisation to give 3,4-bridged indoles. The structures of the azocinoindoles 13, 21, 22 and 35, and the azepinoindole 15 were confirmed by X-ray crystallography. In one case the preparation of a cycloalka[c,d]indole was possible by the irradiation of the α-chloro amide of an indol-3-yl alkanoic acid.