Unexpected Reaction of Ethyl 4-(Chloromethyl)pyrazolo- [5,1-c][1,2,4]triazine-3-carboxylates with Thiourea and Its Mechanism

The reaction of ethyl 4-(chloromethyl)pyrazolo[5,1-c][1,2,4]triazine-3-carboxylates with thiourea in dimethylformamide involves ANRORC rearrangement (Addition of the Nucleophile, Ring Opening, and Ring Closure) followed by N-formylation to give N-{5-(4-oxo-8-phenyl-1,4-dihydropyrazolo[5,1-c][1,2,4]-triazin-3-yl)-1,3-triazol-2-yl}formamides whose structure was confirmed by X-ray analysis. The reaction mechanism has been studied by HPLC/MS.