Acid-catalyzed reaction of 3-aminopyrrole with s-tetrazines: formation of 1H-1,2,4-(triazol-3-yl)pyrimidines via an unprecedented s-tetrazine-ring contraction and concomitant pyrrole-ring expansion

Initial reaction of 3-aminopyrrole with the conjugate acid of 3,6-diphenyl-1,2,4,5-tetrazine gave an intermediate that rearranged to a 1H-1,2,4-(triazol-3-yl)pyrimidine via an unprecedented cascade. In this cascade, the s-tetrazine-ring opened, contracted to a 1,2,4-triazole-ring, and the pyrrole ring expanded to a pyrimidine. Similar results were obtained with three other electronically different s-tetrazines.