2H‑Azirine-2-carbonyl Azides: Preparation and Use as N‑Heterocyclic Building Blocks

2H-Azirine-2-carbonyl azides, new reactive heterocyclic building blocks, were synthesized in high yield by the reaction of sodium azide with 2H-azirine-2-carbonyl chlorides, generated by the Fe­(II)-catalyzed isomerization of 5-chloroisoxazoles. 2-(Azidocarbonyl)-1H-pyrroles, prepared by the Ni­(II)-catalyzed reaction of 2-(azidocarbonyl)-2H-azirines with 1,3-diketones, easily undergo the Curtius rearrangement in boiling tBuOH to give Boc-protected α-aminopyrroles in high yield. Heating of 2-(azidocarbonyl)-1H-pyrroles for a short time in inert solvents leads to the high-yield formation of benzo- and hetero-fused 1H-pyrrolo­[2,3-b]­pyridin-6­(7H)-ones, which are formed via a 6π electrocyclization involving the vicinal aryl or hetaryl substituent and the NC bond of isocyanate, generated by the Curtius rearrangement of the azidocarbonyl group. The Pd-catalyzed cross-coupling reaction of 1-acetyl-2-methyl-3H-pyrrolo­[2,3-c]­isoquinolin-5-yl triflate, easily prepared from the corresponding pyrroloisoquinolone, leads to variously 5-substituted 3H-pyrrolo­[2,3-c]­isoquinolines in excellent yields.