Copper-catalysed decarboxylative alkynylation-cyclization reaction of propargylic cyclic carbonates with nitrile imines to access tetrasubstituted pyrazoles

Herein, we report a robust copper-catalyzed decarboxylative alkynylation-cyclization cascade that enables the efficient synthesis of diverse tetrasubstituted pyrazoles under mild conditions, addressing the long-standing regioselectivity challenge plaguing pyrazole synthesis. Mechanistic studies support a sequential process in which a copper-allenylidene intermediate formed first to mediate the migratory insertion of the propargylic cyclic carbonate, followed by [3+2] cycloaddition with nitrile imine, copper migration, and β-OH elimination.