alpha-Carbonyl Radicals from N-Enoxybenzotriazoles: De Novo Synthesis of 9-Phenanthrols

Abstract

Visible-light-induced energy transfer to N-enoxybenzotriazoles in the presence of hydrogen atom donors or alcoholic solvents led to alpha-carbonyl radicals. The utility of the alpha-carbonyl radicals was demonstrated in intramolecular tandem cyclization and in the synthesis of 9-phenanthrols and their analogues. The mechanistic experiments suggested that quenching of the reactive benzotriazolyl radical by the alcohol was accompanied by the formation of an alpha-hydroxy radical that mediated hydrogen atom transfer or, itself, oxidized into aldehydes.