Asymmetric Allylic Alkylation of Morita-Baylis-Hillman Carbonates

Significance

Herein the authors describe a method for the asymmetric allylic alkylation of racemic Morita-Baylis-Hillman (MBH) carbonates (1) derived from aromatic aldehydes. Reaction with cyanoacetates 2 in the presence of 20 mol% of β-isocupreidine (β-ICPD), a strained quinidine derivative, delivers densely functionalized products of the general type 3, featuring two adjacent quaternary and tertiary stereocenters, in good yields with reasonable diastereo- and enantioselectivities. Due to kinetic resolution in the first conjugate addition A, this process also provides access to highly enantioenriched MBH carbonates (see selected example). Based on experimental observations, the authors proposed a mechanism where β-ICPD acts as bifunctional Lewis base/Brønsted acid catalyst achieving effective face shielding in the second conjugate addition B.