Ruthenium(II)-Catalyzed [2 + 1 + 3] Annulation of 3-Aryl-3-hydroxyisoindolinones with Diazopyrazolones: Step-Economical Synthesis of Spiro[1,3-oxazine-pyrazolones]

Herein, we report the first ruthenium(II)-catalyzed [2 + 1 + 3] annulation of 3-aryl-3-hydroxyisoindolinones with diazopyrazolones. This transformation repurposes the diazo dimer as the key intermediate, traditionally the byproduct hampering the reaction, enabling efficient construction of a series of structurally novel and complex spiro[1,3-oxazine-pyrazolones] in moderate to good yields, in which C-C, C-N, and C-O bonds are formed simultaneously. This strategy demonstrates excellent step economy, broad substrate scope, high chemoselectivity, and remarkable atom economy, only producing environmentally benign water and nitrogen gas as the sole byproducts. Furthermore, derivatization experiments and a gram-scale reaction further validate the synthetic utility of this protocol, establishing an efficient approach for assembling intricate spirocyclic compounds with significant potential applications in pharmaceutical design and functional materials.