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 bisazides 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.