Toward Safer Processes for C−C Biaryl Bond Construction: Catalytic Direct C−H Arylation and Tin-Free Radical Coupling in the Synthesis of Pyrazolophenanthridines
pyrazolo[1,5-f]phenanthridine derivatives has been efficiently synthesized by a short, straightforward sequence. A tandem amine-exchange/heterocyclization of enaminones was successfully applied to the regioselective preparation of 1,5-diarylpyrazole intermediates with structure resemblance to relevant nonsteroidal anti-inflammatory drugs such as celecoxib or tepoxalin. The final key step, cyclization by intramolecular