Phenanthridine Synthesis via a Pd-Catalyzed Direct Arylation/N-Arylation Sequence

Significance

Reported is the synthesis of phenanthridines 3 and benzo[c]phenanthridines 6 via a methodology previously developed by ­Catellani (N. Della Ca’, E. Motti, M. Catellani Adv. Synth. Catal. 2008, 350, 2513) and Lautens (D. A. Candito, M. Lautens Angew. Chem. Int. Ed. 2009, 48, 6713) by coupling of aryl triflates 1 and 4 instead of aryl halides with imines 2 and 5. The palladium-catalyzed domino direct arylation/N-arylation includes the crucial presence of norbornene and proceeds from both EWG- and EDGbearing aryl triflates 1 and 4 and various imines or N-silyl aldimines 2 and 5. This methodology was applied to the synthesis of two benzo[c]phenanthridine alkaloids nitidine 7 and NK109 8. A plausible mechanism is proposed without evidence.