Enantioconvergent Synthesis of Functionalized γ‑Butyrolactones via (3 + 2)-Annulation

A dynamic kinetic resolution of β-halo
α-keto esters
in an asymmetric homoenolate reaction is described. A chiral N-hetereocyclic carbene catalyzes the a3 →
d3-umpolung addition of α,β-enals
to racemic α-keto esters, forming γ-butyrolactones with
three contiguous stereocenters. The addition occurs with high regio-,
diastereo-, and enantiocontrol. This methodology constitutes an intermolecular
DKR process to set three stereocenters during the key bond forming
event.