Mechanistic Evidence for Mild Base-Mediated Intermolecular Trans-Aminoacylations of 1-Acyl-5-amino-1H-1,2,4-triazoles and 5-Amino-1H-1,2,4-triazoles to Afford 5-Acylamino-1H-1,2,4-triazoles

Acylation of 5-amino-1H-1,2,4-triazoles is selective for the nitrogen atom at the ring 1-position of the heterocycle to give 1-acyl-5-amino-1H-1,2,4-triazoles. Thermal rearrangement of 1-acyl-5-amino-1H-1,2,4-triazoles has required high temperatures and concentrated to neat conditions to produce 5-acylamino-1H-1,2,4-triazoles. The mechanism of this rearrangement was thought to be intramolecular and later proposed to be intermolecular based on concentration effects. This work demonstrates that base can promote this rearrangement under mild conditions, and crossover experiments support an intermolecular trans-aminoacylation mechanism.