Dimethylzinc-Mediated Addition of Phenylacetylene to α-Diketones Catalyzed by Chiral Perhydro-1,3-benzoxazines.

An efficient, enantioselective Me2Zn-mediated monoaddition of phenylacetylene to α-diketones in the presence of a chiral perhydro-1,3-benzoxazine ligand is described. At temperatures higher than -20 °C, a kinetic resolution of the resulting α-hydroxy ketone occurs, which greatly improves the enantioselectivity although with moderate chemical yield. The alkynylation of nonsymmetrical aromatic diketones with electronically different substituents on the aromatic rings proceed with high regioselectivity. This procedure allows the preparation of α-hydroxy-α-ynyl ketones as highly enantioenriched materials.