Synthesis of 6-Trichloromethylphenanthridines by Transition Metal-Free Radical Cyclization of 2-Isocyanobiphenyls.

An efficient method for the synthesis of 6-trichloromethylphenanthridines by benzoyl peroxide promoted cyclization reaction of 2-isocyanobiphenyls with carbon tetrachloride is developed. A radical pathway is proposed and evidenced for the reaction mechanism. This reaction tolerates a wide range of functional groups and the resulting 6-trichloromethylphenanthridines can be utilized as a useful synthetic precursor for corresponding 6-substituted phenanthridines.