One-Pot Synthesis of Benzo[]phenanthridine Alkaloids from 7-Azabenzonorbornadienes and Aryl Nitrones.

An efficient synthesis of benzo[]phenanthridine alkaloids via a synergistic combination of C-C bond formation and a cycloaromatization reaction is described. Aryl nitrones react with 7-azabenzonorbornadienes in the presence of a Rh(III) catalyst, providing pharmaceutically useful benzo[]phenanthridine derivatives in good to moderate yields. Using this methodology, highly useful alkaloids such as norfagaronine, norchelerythrine, decarine, norsanguinarine, and nornitidine were prepared in a single step.

A Ruthenium-Catalyzed Cyclization to Dihydrobenzo[]phenanthridinone from 7-Azabenzonorbornadienes with Aryl Amides.

An efficient ruthenium(II)-catalyzed tandem C-C/C-N bond formation with aryl amides and 7-azabenzonorbornadienes has been developed to synthesize -fused dihydrobenzo[]phenanthridinones. The amide group functions as a directing group as well as a leaving group and provides an easy access to the pharmaceutically useful benzo[]phenanthridine alkaloids such as nitidine and fagaronine analogues. The present methodology is compatible with various functional groups with respect to azabicyclic alkenes and aromatic amides.

A Short Total Synthesis of Benzophenanthridine Alkaloids via a Rhodium(III)-Catalyzed C-H Ring-Opening Reaction.

The biologically important naturally available benzophenanthridines were prepared efficiently in three steps with overall good yields. A new synthetic methodology involving a rhodium(III) catalyzed redox-neutral ring-opening of 7-azabenzonorbornadienes with aromatic aldoximes is developed to synthesize the target molecules. The developed C-H ring-opening reaction is highly diastereoselective and compatible with various sensitive functional group substituted aromatic aldoximes as well as substituted 7-azabenzonorbornadienes.