Dynamic Kinetic Asymmetric Cross-Benzoin Additions of β‑Stereogenic α‑Keto Esters

The dynamic kinetic resolution of
β-halo α-keto esters
via an asymmetric cross-benzoin reaction is described. A chiral N-heterocyclic carbene catalyzes the umpolung addition of aldehydes to racemic α-keto esters. The resulting
fully substituted β-halo glycolic ester products are obtained
with high levels of enantio- and diastereocontrol. The high chemoselectivity
observed is a result of greater electrophilicity of the α-keto
ester toward the Breslow intermediate. The reaction products are shown
to undergo highly diastereoselective substrate-controlled reduction
to give highly functionalized stereotriads.