Direct Conversion of 1‑(2-Bromobenzoyl)isoquinolines to Dibenzo[de,g]quinolin-7-ones via Reductive Photocyclization

A series of A/D-ring substituted dibenzo[de,g]quinolin-7-ones was produced from the corresponding isoquinolinones and (2-bromophenyl)acetonitriles in four steps. This represents a convenient approach toward the synthesis of tetracyclic alkaloids. A direct conversion of 1-(2-bromobenzoyl)isoquinolines to dibenzo[de,g]quinolin-7-ones is the key step in the total synthesis. The yield of the reductive photocyclization depends on the position of the substituents at the isoquinolyl ring and the phenyl group. The mechanism of the reductive photocyclization is also discussed.