Bifunctional Brønsted Base-catalyzed [3+3] Annulations of Indolin-2-imines and α,β-Unsaturated Imides: an Enantioselective Approach to α-Carbolinones.

Asymmetric construction of alpha-carbolinones with easily available starting materials has recently attracted considerable attention from the synthesis community, and the development of effective catalysis for this target is in great demand. Here, a bifunctional Bronsted base catalyzed asymmetric [3 + 3] cyclization of indolin-2-imines and alpha,beta-unsaturated N-acylated succinimides was developed by using the strategy of noncovalent bonding catalysis. With this organocatalytic protocol, a variety of tetrahydro-alpha-carbolinones bearing different substituents were synthesized with up to 99% yield and up to 96:4 er.