An Expeditious Route for the Synthesis of Oxazepine Triazolo-β-Lactams through Intramolecular Metal-Free [3 + 2] Azide-Alkyne Cycloaddition

A copper-free intramolecular azide-alkyne cycloaddition reaction of 4-hydroxymethyl-β-lactam with sodium azide has been described. The present approach involves the incorporation of an alkyne moiety through O-alkynylation of 3-hydroxy β-lactam with various propargylic halides. The generality of the method has been demonstrated by treating the corresponding tosylates or mesylates of the hydroxymethyl functionality of a variety of β-lactam-tethered terminal and internal alkynes with sodium azide in a one-pot three-step reaction to furnish novel oxazepane-β-lactam fused triazole scaffolds of diverse interest in good yield.