Copper-Mediated Synthesis of (E)-1-Azido and (Z)-1,2-Diazido Alkenes from 1-Alkene-1,2-diboronic Esters: An Approach to Mono- and 1,2-Di-(1,2,3-Triazolyl)-Alkenes and Fused Bis-(1,2,3-Triazolo)-Pyrazines.

A stereoselective and convenient route has been demonstrated to access (Z)-1,2-diazido alkenes from the corresponding 1,2-diboronic esters via a copper-mediated reaction with sodium azide. Alternately, mono-functionalization was regioselectively carried out with trimethylsilyl azide as an azidation reactant. The in situ conversion of bis-azides to the corresponding bis-triazoles can be readily achieved in the presence of copper sulfate and sodium ascorbate, while the modification of the catalytic system opened a new convenient route to bis-triazolo-pyrazines, a new class of fused heterocycles.