N-Heterocyclic Carbene (NHC)-catalyzed highly diastereo- and enantioselective oxo-diels–alder reactions for synthesis of fused pyrano[2,3-b]indoles

A chiral N-heterocyclic carbene (NHC)-catalyzed Diels–Alder reaction of 2-oxoindolin-3-ylidenes and α-chloroaldehydes was developed for the synthesis of fused pyrano[2,3-b]indoles in good to excellent yields (up to 99%) with high cis-diastereoselectivities (>99:1 dr) and enantioselectivities (up to >99% ee)