Catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines by phase-transfer catalyzed alkylations

Efficient catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines has been achieved via asymmetric alkylation of 1-cyanotetrahydro-β-carbolines using a binaphthyl-modified N-spiro-type chiral phase-transfer catalyst. This is a valuable example of hitherto difficult highly enantioselective alkylations at α-carbon of the cyano group under phase-transfer conditions.