Organocatalytic cascade reactions: towards the diversification of hydroisochromenes and chromenes through two different activation modes.

The organocatalytic enantioselective syntheses of functionalized hydroisochromenes and chromenes by trienamine-mediated [4+2]-cycloaddition/nucleophilic ring-closing and iminium-ion/aminal-mediated oxa-Michael/Michael/nucleophilic ring-closing with 2-nitroallylic alcohols are presented. The corresponding cycloadducts, with up to five stereocenters, are formed in good yield and excellent enantioselectivities. The synthetic applications of the obtained products have been demonstrated.