Rearrangement of 1-amino- and 1-alkylamino-pyrazoles to 5-aminopyrazoles

Abstract

Rearrangement of 1-aminopyrazole and 1-alkylaminopyrazoles into the corresponding 5-aminopyrazoles has been achieved in 48% aqueous hydrobromic acid. The reaction, occurring through a ring opening–ring closure mechanism, constitutes a new and unambiguous procedure for the preparation of 1-substituted 5-aminopyrazoles. The products have been identified on the basis of ¹H and ¹³C n.m.r. spectroscopic results and comparison with authentic samples.