Mechanistic Insights into the Ligand-Directed Divergent Synthesis of 2-Benzazepine Derivatives via Ni-Catalyzed...

The detailed mechanisms of Ni-catalyzed ligand-controlled cyclization/cross-coupling of o-bromobenzenesulfonyl acrylamide (1a) with trifluoromethyl alkene were investigated by DFT calculations. The computational results support a single-electron reduction of Ni^II precatalyst to give BrNi^IL species, which would react with 1a via oxidative addition to afford the (Ar)Ni^IIILBr₂ complex. The subsequent cyclizations did not proceed until (Ar)Ni^IIILBr₂ was reduced to the key (Ar)Ni^IL complex. For the bpy-involving reaction, the subsequent steps include nucleophilic attack to the carbonyl carbon atom, N-C bond breaking, intramolecular migratory insertion, as well as concerted C-C cross-coupling and β-F elimination. While the ligand of terpyridine promotes the 7-endocyclization followed by stepwise migratory insertion and β-F elimination to afford 2-benzazepine 2,5-dione. For both reactions, a theoretical study implied that the most favorable mechanism involved a Ni^I-Ni^III-Ni^I catalytic cycle. The origins of the chemoselectivity, coupled with the factors responsible, were addressed.