Base‐Catalyzed Nucleophilic Addition of Oxindoles to 3‐Diazo Oxindoles: An Efficient Approach for the Synthesis of Functionalized Isatin‐Hydrazones

Abstract A highly efficient catalytic nucleophilic addition of 3‐substituted oxindoles to 3‐diazo oxindoles has been achieved. This method relies on an organic base catalysis system, which can simultaneously activate 3‐substituted oxindoles as a nucleophile and the diazo compounds as a strong N ‐terminal electrophile. Importantly, this approach could yield a broad array of functionalized isatin‐hydrazones featuring an adjacent tetrasubstituted carbon centre of the N(sp3) atom.