Enantio- and Diastereoselective Synthesis of Chromeno[4,3‑b]pyrrole Derivatives Bearing Tetrasubstituted Chirality Centers through Carbene Catalyzed Cascade Reactions

An NHC-catalyzed cascade cycloaddition reaction is developed for quick access to structurally sophisticated tetrahydro­chromeno­[4,3-b]­pyrrole derivatives. A sterically congested tetrasubstituted chirality carbon center is formed during the cyclization process. All the α-, β-, and carbonyl carbons of the enal substrates are functionalized in chemo- and stereoselective fashion. The multicyclic chromeno­[4,3-b]­pyrrole products are generally afforded in good yields with excellent enantio- and diastereoselectivities. Heavily substituted pyrroline derivatives can be afforded from the chiral products through simple protocols.