Organocatalytic domino Michael/cyclization reaction: efficient synthesis of multi-functionalized tetracyclic spirooxindoles with multiple stereocenters

The asymmetric domino reaction of various 3-nitro-2H-chromene derivatives 2 to 3-isothiocyanato oxindole 3 with moderate to good enantioselectivities, employing readily available bifunctional thiourea 1d as the organocatalyst, was described. A series of chiral multi-functionalized tetracyclic spiro [chromeno[3,4-c] pyrrole-1,3'-indoline] derivatives with four vicinal chiral carbon centers including two quaternary stereocenters were successfully prepared. Notably, the products 5 could be cleanly converted to the compounds 4 in ethanol under mild conditions.