Enantioselective organocatalytic synthesis of the chiral chromenes by domino oxa-Michael-aldol reaction

The proline based chiral organocatalyst has been found to be an efficient catalyst for the facile synthesis of substituted 2-aryl-2H-chromenes-3-carbaldehyde. We envisioned that the iminium interaction between chiral amino catalysts and α,β-unsaturated carbonyl group was beneficial along with thiourea group as hydrogen bond donor, heterocyclic amines as general base in the domino oxa-Michael-aldol reaction. This catalytic system provided the products in good to high yields (73%–96%) with excellent enantioselectivity (up to 97%) and reasonable reaction time. The atom economy, high yield and mild reaction conditions are some of the important features of this protocol.