Enantioselective Assembly of Spirolactones through NHC-Catalyzed Remote γ-Carbon Addition of Enals with Isatins.

A chiral N-heterocyclic carbene (NHC)-catalyzed formal [4 + 2] annulation of β-methyl substituted enals with isatins was developed to construct six-membered spirolactones bearing highly congested quaternary carbon stereocentersin good yields and high enantioselectivities. The strategy realized a challenging remote γ-carbon addition of enals and chiral control of β-methyl substituted enals in the presence of the NHC catalyst only.