Sustainable multicomponent synthesis of C-4 sulfenylated pyrazoles <i>via</i> sodium thiosulfate-promoted tandem cyclocondensation and C–H sulfenylation

We report a novel and environmentally benign multicomponent reaction (MCR) strategy for the synthesis of C-4 sulfenylated pyrazoles promoted by Na₂S₂O₃·5H₂O. This metal-free, one-pot protocol enables the simultaneous formation of two C-N bonds and one C-S bond through a cascade of cyclocondensation and direct C-H sulfenylation. A wide range of aryl and alkyl hydrazines and disulfides are efficiently converted to the corresponding products in good to excellent yields (72-94%) under sustainable conditions. DMSO plays a dual role as both the reaction medium and a modulator facilitating thiyl radical generation, which is essential for achieving regioselective C-4 sulfenylation. Compared to previously reported metal-catalyzed methods, this protocol offers high atom economy, broad substrate scope, and reduced environmental footprint, aligning well with the principles of green chemistry and advancing sustainable synthetic methodologies in heterocyclic chemistry.