One‐Pot Enantioselective Synthesis of 3‐Nitro‐2 H ‐chromenes Catalyzed by a Simple 4‐Hydroxyprolinamide with 4‐Nitrophenol as Cocatalyst

The asymmetric domino oxa‐Michael–Henry reaction of salicylaldehyde derivatives with trans ‐β‐nitro olefins catalyzed by a readily available trans ‐4‐hydroxy‐ L ‐prolinamide with 4‐nitrophenol as an effective cocatalyst is presented. The corresponding 3‐nitro‐2 H ‐chromenes were obtained in moderate to excellent yields (up to 99 %) and with up to 90 % ee under mild conditions. In addition, a preliminary study shows that this organocatalytic system is able to promote the domino aza‐Michael–Henry reaction of 2‐formylpyrrole derivatives with trans ‐β‐nitro olefins to give chiral 2‐nitro‐3 H ‐pyrrolizines.