2<i>H</i>‑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.