Coinage Metal-Catalyzed Divergent Heterocyclizations of Underexplored N-Propargyl Hydrazides

Herein, we disclose metal-catalyzed tunable annulations of uncharted alkyne-tethered hydrazides for the divergent preparation of diazacyclic frameworks. Cationic gold facilitates the O-cyclization, providing valuable 1,3,4oxadiazine scaffolds with total selectivity, whereas silver catalysis promotes controlled N-cyclization to access N-acyl pyrazoles. Furthermore, density-functional-theory-based theoretical investigations support two different pathways (ionic versus radical) operating in the catalytic heterocyclization reaction of the same N-propargyl hydrazide substrate.