N-Heterocyclic carbene-catalyzed [4 + 2] cyclization of α-chloroaldehydes and aurones: Highly enantioselective synthesis of benzofuran-fused dihydropyran-2-ones

The chiral N-heterocyclic carbene-catalyzed [4 + 2] annulation of α-chloroaldehydes and aurones was developed, giving the corresponding benzofuran–fused dihydropyranones in good to high yields with good diastereoselectivities and excellent enantioselectivities. The catalytic cycle features with the generation of enolate from chloroaldehdye and its following [4 + 2] cycloaddtion with aurones.