Facile access to 2-aryl-3-nitro-2H-chromenes and 2,3,4-trisubstituted chromanes

Using salicylaldehydes and beta-nitrostyrenes as starting materials, 2-aryl-3-nitro-2H-chromenes were prepared in good yields (up to 83%) through the combination of 30 mol% of pyrrolidine-benzoic acid catalyzed tandem oxa-Michael-Henry reactions in refluxing ethanol. Additionally, the Michael reactions of 2-aryl-3-nitro-2H-chromenes with acetone were also performed by the same catalytic combination in brine to give 2,3,4-trisubstituted chromanes up to 86% yield with excellent stereoselectivities. The structures of 2-aryl-3-nitro-2H-chromenes and 2,3,4-trisubstituted chromanes are confirmed by X-ray single crystal diffraction analysis. The reductive amination of a suitable 2,3,4-trisubstituted chromane with Zn/HOAc affords a fused tricyclic amine in 92% yield.