Asymmetric Synthesis of Polysubstituted 4-Amino- and 3,4-Diaminochromanes with a Chiral Multifunctional Organocatalyst

A series of multifunctional catalysts with two chiral diaminocyclohexane units were developed and successfully applied in the asymmetric oxa-Michael-aza-Henry cascade reaction of salicylaldimines with nitroolefins. This approach provides a simple and efficient entry to polysubstituted chiral 4-aminobenzopyrans with three consecutive stereocenters and in high yield (up to 97%) with excellent stereoselectivity (up to 98% ee and >99:1 dr). Facile access to the nonsymmetric optically pure 3,4-diaminochromanes was also obtained.