Pd-Catalyzed Synthesis of Phenanthridinones by Double C-H Activation

Significance

Reported is the synthesis of phenanthridinones 3 from N-methoxybenzamides 1 and arenes 2 via a double Pd-catalyzed C-H ­activation approach. The substrate scope with ­respect to the N-methoxybenzamide was well explored, with EDGs and EWGs well tolerated at various ring positions. The scope of the arene coupling partner was poorly studied, and this reaction appears to suffer from the same drawback as many C-H activation processes, that is the requirement to use simple, symmetrical arenes in order to obtain high yield and regioselectivity. Deprotection of the methoxy group was demonstrated in one case by photolysis in methanol. A plausible mechanism involving Pd⁰/Pd^II and Pd^II/Pd^IV catalytic cycles was proposed based on related processes, but without evidence.