Catalytic asymmetric conjugate addition of Grignard reagents to coumarins--synthesis of versatile chiral building blocks.

A new protocol for the Cu-catalysed asymmetric conjugate addition of Grignard reagents to coumarins has been developed. The corresponding products are formed in high yields and enantioselectivities. Through a sequential protocol involving conjugate addition followed by nucleophilic ring opening of the chiral enolate, chiral esters and amides are readily accessible.