Ring-chain isomerism of ethyl 7-polyfluoroalkyl-7-hydroxy-4,7-dihydro[1,2,4]triazolo[1,5-a]pyrimidine-6-carboxylates

Cyclisation of ethyl 2-ethoxymethylidene-3-oxo-3-polyfluoroalkylpropionates with 3-amino-1H-[1,2,4]triazole gives ethyl 7-polyfluoroalkyl-7-hydroxy-4,7-dihydro[1,2,4]triazolo[1,5-a]pyrimidine-6-carboxylates that are subject to ring–chain isomerisation in solution, depending on the solvent and the length of the polyfluoroalkyl substituent, to yield ethyl 3-polyfluoroalkyl-3-oxo-2-{([1,2,4]triazol-3-yl)aminomethylidene}propionates via heterocyclic ring opening at the C(7)–N(8) bond.