Tandem Condensation–Cycloaddition of Propargylic Amines with α‑Azido Ketones and β‑Alkoxy-γ-Azido Enones

α-Azido ketones and their vinylogous relatives
β-alkoxy-γ-azido
enones are versatile building blocks for constructing diverse heterocyclic
products, but are prone to azide decomposition. Here, we report their
condensation with propargylic amines and investigate the fate of the
intermediate azido-enamine condensation products, both experimentally
and theoretically. Efficient intramolecular cycloaddition was observed
for electron-poor azide substrates, and a range of diversely substituted
[1,2,3]triazolo[1,5-a]pyrazine products is reported.
For electron-rich substrates, azide decomposition predominated. Computational
modeling of possible pathways from the azido-enamine intermediates
revealed two alternative mechanisms for azide decomposition, which
were consistent with observed side products.