C-H functionalization C-H/C-N activation C-N ? bond cleavage C-S formation C–H acidity C–H bond cleavage C–N bond cleavage C–O activation DFT study DMAc DMF HERON reaction Michael acceptor N N-(1-naphthyl)acetamide N-dimethylacetamide N-dimethylformamide N-heterocyclic carbene N-heterocyclic carbenes (NHCs) N–C activation Pd-catalysis Suzuki-Miyaura Winkler-Dunitz parameters [2+2+2] annulation activation acyl transfer acylative cross-coupling addition reaction additivity principle alkynes