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

2-Azirine-2-carbonyl azides, new reactive heterocyclic building blocks, were synthesized in high yield by the reaction of sodium azide with 2-azirine-2-carbonyl chlorides, generated by the Fe(II)-catalyzed isomerization of 5-chloroisoxazoles. 2-(Azidocarbonyl)-1-pyrroles, prepared by the Ni(II)-catalyzed reaction of 2-(azidocarbonyl)-2-azirines with 1,3-diketones, easily undergo the Curtius rearrangement in boiling BuOH to give Boc-protected α-aminopyrroles in high yield. Heating of 2-(azidocarbonyl)-1-pyrroles for a short time in inert solvents leads to the high-yield formation of benzo- and hetero-fused 1-pyrrolo[2,3-]pyridin-6(7)-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-3-pyrrolo[2,3-]isoquinolin-5-yl triflate, easily prepared from the corresponding pyrroloisoquinolone, leads to variously 5-substituted 3-pyrrolo[2,3-]isoquinolines in excellent yields.