Preparation of Phenanthridines from o-Cyanobiaryls via Addition of Organic Lithiums to Nitriles and Imino Radical Cyclization with Iodine.

Simple treatment of 2-cyanobiaryls with methyllithium, ethylmagnesium bromide, butyllithium, phenyllithium, p-methylphenyllithium, etc., followed by the reaction with water and then with molecular iodine at 60 °C provided efficiently 6-methyl-, 6-ethyl-, 6-butyl-, 6-phenyl, 6-( p-methylphenyl)phenanthridines, etc., in good yields, respectively. Here, imines formed through the addition of carbanion onto the nitriles reacted with molecular iodine to form N-iodoimines smoothly, and their warming treatment induced the formation of imino radicals that smoothly cyclized onto the aryl group to give 6-alkyl- and 6-arylphenanthridines.