Synthesis and Thermolysis of Heterocyclic 3-Aza-3-ene-1,5-diynes<sup>1</sup>

Simple, acyclic 3-aza-3-ene-1,5-diynes undergo an aza-Bergman rearrangement to a fleeting 2,5-didehydropyridine (2,5-ddp) intermediate that rapidly ring-opens to β-alkynylacrylonitrile products. In an effort to access longer-lived 2,5-ddp intermediates, we have prepared heterocyclic 3-aza-3-ene-1,5-diynes. The thermolysis of one such heterocyclic aza-enediyne does not afford products derived from trapping a 2,5-ddp intermediate but rather cyclopropanes that appear to arise from a carbene intermediate and a product that appears to be a trapping product from a 2,3-ddp intermediate.