Stereodivergent assembly of tetrahydro-γ-carbolines via synergistic catalytic asymmetric cascade reaction

Enantiomerically enriched indole-containing heterocycles play a vital role in bioscience, medicine, and chemistry. As one of the most attractive subtypes of indole alkaloids, highly substituted tetrahydro-gamma-carbolines are the basic structural unit in many natural products and pharmaceuticals. However, the syntheses of tetrahydro-gamma-carbolines with high functionalities from readily available reagents are significant challenging. In particular, the stereodivergent syntheses of tetrahydro-gamma-carbolines containing multi-stereogenic centers remain quite difficult. Herein, we report an expedient and stereodivergent assembly of tetrahydro-gamma-carbolines with remarkably high levels of stereoselective control in an efficient cascade process from aldimine esters and indolyl allylic carbonates via a synergistic Cu/Ir catalyst system. Control experiments-guided optimization of synergistic catalysts and mechanistic investigations reveal that a stereodivergent allylation reaction and a subsequent highly stereoselective iso-Pictet-Spengler cyclization are the key elements to success.