N-Heterocyclic carbene-catalyzed enantioselective hetero-[10+2] annulation

High-order cycloaddition reactions are useful for the construction of polycycles in a single step, but versions that induce asymmetry are limited. Here the authors report the construction of asymmetric polycycles via N-heterocyclic carbene-catalyzed hetero-[10 + 2] cycloaddition of indole-2-carbaldehydes with trifluoromethyl ketone derivatives. Higher-order cycloadditions are a powerful strategy for the construction of polycycles in one step. However, an efficient and concise version for the induction of asymmetry is lacking. N-heterocyclic carbenes are widely used organocatalysts for asymmetric synthesis and could be an ideal choice for enantioselective higher-order cycloadditions. Here, we report an enantioselective [10 + 2] annulation between catalytically formed aza-benzofulvene intermediates and trifluoromethyl ketone derivatives. This protocol exhibits a wide scope, high yields, and good ee values, reflecting a robust and efficient higher-order cycloaddition. Density functional theory calculations provide an accurate prediction of the reaction enantioselectivity, and in-depth insight to the origins of stereocontrol.