Visible-Light-Induced Intramolecular Dehydrogenative Cyclization of o-Aryl Benzaldehydes

A visible-light-induced dehydrogenative cyclization of o-aryl benzaldehydes has been developed by using bench-stable N-aminopyridinium salt as both a HAT reagent and a mild oxidant, which affords a wide range of fluorenones with diverse substitution patterns in moderate to excellent yields. Furthermore, this protocol is applicable to the de novo synthesis of the natural product Nobilone. Mechanism investigation supports a photoinduced homocleavage of N-aminopyridinium salt and a radical chain process.