Regioselective Synthesis of Indole-Fused Seven-Membered N-Heterocycles via Photoredox-Catalyzed Intramolecular Cyclization

DFT Study on Mechanism of Ni-Al Bimetallic-Catalyzed C-H Cyclization to Construct Tricyclic Imidazoles: Roles of NHC Ligand and AlMe3

The mechanism of the Ni-Al bimetallic-catalyzed C-H cyclization to construct tricyclic imidazoles is investigated using density functional theory calculations. The calculation result shows that the reaction mechanism involves sequential steps of substrate coordination, ligand-to-ligand hydrogen transfer (LLHT), and C-C reductive elimination to produce the final product tricyclic imidazole. The LLHT step is calculated to be the rate-determining step. The oxidative addition of the benzimidazole C-H bond to the Ni center and the insertion of the alkene into the Ni-H bond occur concertedly in the LLHT step. The effects of N-heterocyclic carbene (NHC) ligands and AlMe3 on the reactivity and regioselectivity were also analyzed. These calculation results shed light on some ambiguous suggestions from experiments.

Synthesis of Azepino[4,5-b]indole via Ring Expansion of Tetrahydro-β-carbolines Ammonium Ylide

The formal cyclization strategy was generally used to construct azepino[4,5-b]indole. Herein, we reported a novel and expeditious protocol for the synthesis of quaternary carbon azepino[4,5-b]indole via ring expansion of ammonium ylide, which was formed by the reaction of tetrahydro-β-carbolines with the diazo compound. The easily available substrates, mild reaction conditions, and broad functional tolerance rendered this method a practical strategy that may significantly afford an efficient method of scaffold hopping in drug discovery.