N-(Propargyl)diazenecarboxamides for ‘click’ conjugation and their 1,3-dipolar cycloadditions with azidoalkylamines in the presence of Cu(II)

Propargyl functionalized diazenes 1 were prepared by two different approaches and were examined as alkyne click components in copper-catalyzed azide–alkyne cycloadditions (CuAAC) with 2-(azidomethyl)pyridine 5a and four α-azido-ω-aminoalkanes C2–C5 (5b–e). Whereas the reactions with azidoalkylamines 5b–e reached completion with copper(II) sulfate without the need of reducing agent typically in no more than few minutes, 2-(azidomethyl)pyridine 5a required the addition of metallic copper and much longer reaction times (2–24 h). This difference in the reactivity was studied and addressed in terms of base effect and proximity effect to CuAAC.