Catalytic Asymmetric Protonation of Chiral Calcium Enolates via 1,4-Addition of Malonates

Catalytic asymmetric protonation of chiral calcium enolates was performed. Chiral calcium enolates, prepared in situ from imides and malonates via 1,4-addition in the presence of catalytic amounts of Ca(OEt)(2), Ph-PyBox, and achiral phenol, were smoothly protonated to afford adducts bearing tertiary asymmetric carbons in high yields with high enantioselectivities. The adducts were readily converted to optically active 2-substituted 1,5-dicarboxylic acid derivatives.