Copper-Catalyzed Sulfonyl Azide–Alkyne Cycloaddition Reactions: Simultaneous Generation and Trapping of Copper–Triazoles and −Ketenimines for the Synthesis of Triazolopyrimidines

First simultaneous generation and utilization of both copper–triazole and −ketenimine intermediates in copper-catalyzed sulfonyl azide–alkyne cycloaddition reactions is achieved for the one-pot synthesis of triazolopyrimidines via a novel copper-catalyzed multicomponent cascade of sulfonyl azides, alkynes, and azirines. Significantly, the reaction proceeds under very mild conditions in good yields.