Synthesis of phenanthridines by radical C-aryl-C-aryl coupling

Treatment of N-(o-bromobenzyl)anilines with 1-3 equivalent amounts of n-tributyltinhydride, in the presence of 0.5 to 0.6 mol equiv. of AIBN, results in the formation of phenanthridines in good yields. The mechanism of the oxidation step is probed with a deuterated aniline derivative and azobiscyclohexylcarbanonitrile (ABCN) as the initiator. It is shown that the carbon centred radical derived from the latter does not act as the hydrogen abstracting species. Copyright (C) 1996 Elsevier Science Ltd