Base‐Mediated Diastereoselective Aza/Oxa‐Michael Approach to Spiro‐Pyrazolone and Spiro‐Oxindole Derivatives Through [4 + 2] Spiro‐Annulation

A metal‐free, base‐catalyzed double Michael diastereoselective [4 + 2] annulation reaction of para ‐quinone methides with alkylidene pyrazolones and isatin‐derived N ‐Boc ketimines or isatylidine malonitriles has been developed, leading to biologically inspired spiro‐heterocyclic derivatives under mild reaction conditions in a short reaction time. This strategy involves an atom‐economic transformation that generates three contiguous stereocenters, including a quaternary spiro‐center, in good to excellent yield (up to 94%) with excellent diastereoselectivities (up to >20:1 dr ).