Synthesis of spirocyclic 3Н-pyrrol-4-amines from 2H-azirines and 1-sulfonyl-1,2,3-triazoles

The first derivatives of 3H-pyrrol-4-amines spiro-fused with fluorene or anthrone were synthesized in a Rh2(OAc)4-catalyzed reaction of 1-sulfonyl-1,2,3-triazoles with 2H-azirines. The reaction proceeds through 1,4-diazahexa-1,3,5-triene intermediates, which under the conditions employed cyclize to stable at room temperature 1,2-dihydropyrazines. At elevated temperatures, 1,2-dihydropyrazines are in ring-chain equilibrium with 1,4-diazahexa-1,3,5-trienes, which undergo irreversible 5-exo-trig cyclization, leading to spirocyclic derivatives of 3H-pyrrol-4-amine.