Ni-Catalyzed Ligand-Controlled Selective 5-Exo and 6-Endo Cyclization/Cross-Couplings Involving an Unusual 1,2-Aryl Migration
Miao Yang, Ning Liu, Zhanhao Zhang, Yuanbin She, Yun‐Fang Yang
Abstract
Nickel-catalyzed ligand-controlled reductive dicarbofunctionalization of alkenes provides a regiodivergent synthetic strategy for constructing five- and six-membered benzo-fused lactams bearing all-carbon quaternary centers. Density functional theory (DFT) calculations have been carried out to elucidate the detailed mechanisms of this 5-exo vs 6-endo Heck cyclization/cross-coupling reaction. The computational results suggest that 5-exo is favored over 6-endo in the cyclization step with either the bidentate bipyridine ligand or the tridentate C6-carboxylic acid-modified bipyridine ligand. Multiple mechanistic pathways involving different Ni oxidation states might be operative for the formation of the 5-exo Heck cyclization/cross-coupling product with the bidentate bipyridine ligand. By contrast, the tridentate C6-carboxylic acid-modified bipyridine ligand favors the NiIII pathway, and the 5-exo cyclization NiIII-alkyl intermediate undergoes an unusual 1,2-aryl migration to form the 6-endo ring expansion cross-coupling product.