Isothiourea-Catalyzed Enantioselective Synthesis of Tetrahydro-α-carbolinones

An isothiourea-catalyzed enantioselective annulation protocol using indolin-2-imines with a series of α,β-unsaturated p-nitrophenyl esters for the synthesis of tetrahydro-α-carbolinones was developed. Using 5 mol % of the isothiourea HyperBTM as the Lewis base catalyst, this process allows the enantioselective preparation of a range of C(4)-substituted tetrahydro-α-carbolinones in good to excellent yield and with high enantioselectivity (20 examples, 32–99% yield and up to 99:1 er).