Copper-catalyzed 2,3-dihydro-1,2,4-triazoles synthesis through [3+2]-cycloaddition of nitrile ylides with azodicarboxylates

A copper-catalyzed three-component reaction of diazo compounds, nitriles, and azodicarboxylates to construct 2,3-dihydro-1,2,4-triazoles is reported. Key to the success is the utilization of azodicarboxylates to trap the in-situ formed nitrile ylides from diazo compounds by [3 ​+ ​2]-cycloaddition. Both the acceptor-only and donor-acceptor diazo compounds are all tolerated to the strategy. The synthetic value of this protocol is illustrated by gram-scale synthesis and valuable transformation of the obtained 2,3-dihydro-1,2,4-triazoles.