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 α-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 Brønsted
base catalyzed asymmetric [3 + 3] cyclization of indolin-2-imines
and α,β-unsaturated N-acylated succinimides
was developed by using the strategy of noncovalent bonding catalysis.
With this organocatalytic protocol, a variety of tetrahydro-α-carbolinones
bearing different substituents were synthesized with up to 99% yield
and up to 96:4 er.