Stereoselective Synthesis of Hydropyrano[3,2‐b]indoles via Organocatalytic Asymmetric Inverse‐Electron‐Demand Oxa‐Diels–Alder Reaction

Enantio‐ and diastereoselective inverse‐electron‐demand oxa‐Diels–Alder reactions are described between (Z)‐2‐ylideneoxindoles and aldehydes in the presence of a chiral secondary amine catalyst. The corresponding hydropyrano3,2‐b]indoles are produced in up to 77% yield with up to 99% ee. Convenient synthetic transformations of the products readily lead to pharmacologically interesting scaffolds bearing multiple functional groups. This method may also provide an alternative approach for the asymmetric synthesis of 2‐spirocyclo‐3‐oxindoles.