Enantioselective Synthesis of Tryptamines and Tetrahydro-β-carbolines

Significance

The enantioselective Michael addition of nitro-olefins to indoles to give products which are converted into chiral tryptamines and tetrahydro-β-carbolines is reported. The enantioinduction is catalyzed by hydrogen bonding by a chiral bis-sulfonamide, prepared from the readily available corresponding chiral diamine. The scope and the yields of the reaction are modest. Although the enantioselectivity is low to moderate, recrystallization gives >98% enantiopure products. With the assistance of the X-ray crystal structure of the chiral sulfonamides, an intermediate for the reaction is proposed.