Cobalt-Catalyzed Hydrogen-Bond-Promoted Tandem Cyclization and Oxygen Migration: Access to Sterically Congested Fused Tetrahydro-β-Carbolines

A cobalt-catalyzed, hydrogen-bond-promoted strategy for the synthesis of sterically congested fused tetrahydro-β-carbolines bearing quaternary carbon centers is reported. This transformation employs tryptamine-derived isocyanides and anthranils as readily available building blocks and proceeds through a tandem oxygen migration and cyclization process with high atom economy. Moderate to good yields are obtained for structurally diverse products. Water plays a crucial role by providing a hydrogen-bonding environment and serving as a proton shuttle to facilitate the reaction process, which is supported by isotope-labeling experiments and DFT calculations.