Competitive intramolecular C-C vs. C-O bond coupling reactions toward C6 ring-fused 2-pyridone synthesis

An interesting competitive C-C vs. C-O bond coupling reaction on N,3,5-trisubstituted pyridones is reported. These coupling reactions provided selective access to C- or O-ring-fused pyridones, both at the challenging C-6-pyridone position. 1,6-C-Annulated pyridones were generally achieved in good yields with excellent chemoselectivity under Pd(0) conditions. On the other hand, full C-6-regioselective Csp(2) aryloxylation was achieved under oxidative coupling promoted by silver salts to access 5,6-O-annulated pyridones. Based on various experiments and observations, mechanistic evidence of these competitive reactions was provided and it was proposed that C-O bond formation proceeded through radical cyclization. These processes were performed under mild reaction conditions and offer an efficient and attractive methodology to selectively access a large scope of C-arylated and O-arylated pyridones of biological interest.