Asymmetric [1+4] Cyclization of α‐Chloro Hydrazones for the Synthesis of Pyrazoline‐spirooxindoles

Comprehensive Summary We reported an organocatalytic enantioselective [1+4] annulation between 3‐isothiocyanato oxindoles and α‐chloro hydrazones. α‐Halo hydrazones have emerged as valuable precursors for nitrogen‐containing scaffolds, yet their asymmetric transformations remained constrained to two catalytic modes: metal‐catalyzed processes requiring chiral ligands, and N ‐heterocyclic carbene catalysis that relies on carbonyl partners to establish stereocontrol. Therefore, we sought to develop a fundamentally different asymmetric strategy rooted in organocatalysis. 3‐Isothiocyanato oxindoles offered an ideal platform for this purpose. While extensively applied as C3 synthons in asymmetric transformations, their NCS functionality also behaved pseudo‐halide character, rendering them latent C1 synthons—an intriguing but previously unrealized reactivity mode in asymmetric catalysis. In this work, we demonstrated the first enantioselective application of 3‐isothiocyanato oxindoles as C1 synthons. Squaramide‐type hydrogen bond‐based organocatalyst established a well‐defined chiral environment, ensuring efficient stereocontrol during the reaction. The reaction proceeded smoothly under mild conditions and exhibited broad functional‐group tolerance. The resulting pyrazoline–spirooxindoles were obtained in consistently high yields and excellent enantioselectivities. This study established a distinct organocatalytic mode for asymmetric transformations of α‐chloro hydrazones and expanded the synthetic utility of NCS‐based electrophiles in enantioselective synthesis.