Energy transfer-driven regioselective synthesis of functionalized phenanthridines by visible-light Ir photocatalysis

A photocatalytic strategy for regioselective synthesis of phenanthridine derivatives from N-(2-arylbenzylidenamino)pyridinium salts has been developed. Utilization of an Ir photocatalyst, [Ir{dF(CF3)ppy}2(dtbbpy)]PF6 (dF(CF3)ppy = 3,5-difluoro-2-(5-(trifluoromethyl)-2-pyridyl)phenyl, dtbbpy = 4,4’-di-tert-butyl-2,2’-bipyridine), is a key to successful reactions. The excited Ir catalyst does not serve as a 1e-redox reagent but as an energy donor toward the pyridinium salts. The present system can be also applied to one-pot synthesis of Trisphaeridine, an anti-cancer drug.