Copper-Catalyzed Aza-Iminosydnone-Alkyne Cycloaddition Reaction Discovered by Screening

The chemistry and reactivity of mesoionic compounds represent a chemical space largely unexploited. Using a MS-based screening approach, the reactivity of mesoionics toward terminal alkynes under copper catalysis has been explored. This approach led to the discovery of new reactions allowing chemoselective ligation of the two reaction partners and, simultaneously, the release of a fragment molecule. The reactivity of aza-iminosydnones allowing the selective formation of 1,2,3 triazoles or hydrazineylidene-propanal derivatives from alkynes was revealed. This copper-catalyzed reaction was found to be under the control of copper-ligand and alkyne structures. The scope of the reactions and mechanistic investigations are presented.