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

ABSTRACT: 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 con-stitutes an intermolecular DKR process to set three stereocenters during the key bond forming event. Dynamic kinetic asymmetric transformations are potentmethods to generate functionalized and stereochemically defined products from racemic starting materials, and a number of enzymatic and chemocatalytic reactions have been put forward utilizing this paradigm.1 Concomitant with the burgeoning number of dynamic methodologies has been an increase in the stereochemical complexity generated in thes