A Cooperative N-Heterocyclic Carbene/Chiral Phosphate Catalysis System for Allenolate Annulations

The highly enantioselective NHC-catalyzed [3+2] annulation reaction with alpha,beta-alkynals and alpha-ketoesters has been developed. A new mode of cooperative catalysis involving the combination of a chiral Bronsted acid and a C-1-symmetric biaryl saturated-imidazolium precatalyst was required to generate the desired gamma-crotonolactones in high yields and levels of enantioselectivity.