Bischler-Napieralski Synthesis of Phenanthridines

Abstract

Reported is the Hendrickson reagent mediated Bischler-Napieralski synthesis of substituted phenanthridines. A mechanism following the classical proposal is given, whereby the Hendrickson reagent reacts with the amide group to form structure A, which then participates in a Friedel-Crafts reaction with the remote aromatic ring. This is consistent with the observed substituent effects, for example, R³ = 3-NO2 fails to undergo reaction. The reaction is not affected by the electronics of the amide; however, it is sensitive to steric effects.