Azirine-triazole hybrids: selective synthesis of 5-(2H-azirin-2-yl)-, 5-(1H-pyrrol-2-yl)-1H-1,2,3-triazoles and 2-(5-(2H-azirin-2-yl)-1H-1,2,3-triazol-1-yl)pyridines.

Azirine-triazole hybrids, 1-R-5-(3-aryl-2H-azirin-2-yl)-1H-1,2,3-triazoles, were selectively synthesized by reaction of 1-(3-aryl-2H-azirin-2-yl)-2-(triphenylphosphoranylidene)ethanones with tosyl and (E)-2-benzoylvinyl azides in high yields at rt. The reaction with 2-azidopyridine makes it possible to obtain azirine-triazole-pyridine hybrids, albeit in moderate yields, at 170 °C. The mechanism and selectivity of the reaction of α-carbonylphosphoranes with azides are discussed on the basis of DFT calculations. According to the calculation, the reaction of α-carbonylphosphoranes with model mesyl azide, leading to 1,5-disubstituted triazoles proceeds via a non-concerted cycloaddition, while the reaction leading to 1,4-disubstituted triazoles proceeds via a concerted azide cycloaddition, but through the transition state which has much higher energy. In contrast to the reaction of α-(triphenylphosphoranylidene)ketones with TsN3, the reaction with TfN3 yields the α-diazo ketones. Ni-Catalyzed reaction of azirinyl-1,2,3-triazoles with acetylacetone provides pyrrole-triazole and pyrrole-triazole-pyridine hybrids in good yields under mild conditions.

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.