2-Acylcycloalkanones having polyfluoroalkyl groups react with guanidine, urea, thiourea, methylisothiourea, benzamidine, guanylthiourea, dicyanodiamide, and trifluoroacetylurea by Lewisacid catalysis to form the corresponding 5,6-oligomethylene pyrimidines. A decrease in the yields along with increase of polyflyoroalkyl substituent length in the molecule of the starting 1,3-diketone was observed in the case of reagents with lower nucleophilicity (urea, thiourea, dicyanodiamide). The pyrimidines obtained from aromatic aldehydes showed E-configuration with respect to the arylidene double bond. Tautomeric structures as a function of the substituent in 2 position in the pyrimidine ring both in liquid and solid state were investigated by X-ray diffraction, IR and NMR spectroscopy.
The reaction between 2-trifluoroacetylcycloalkanones and methylhydrazine or phenylhydrazine exclusively yields 3-CF3-pyrazoles. When the chain length of the polyfluorinated substituent in RFC(O) group increases, 5-RF-pyrazoles are isolated. The reaction of 2-trifluoroacetylcyclohexanone with 2-hydrazinopyradine gives 5-hydroxypyrazoline, an intermediate in the formation of 5-CF3-pyrazoles. The regiochemistry of the condensation is probably controlled by the nucleophilicity of the terminal nitrogen in the mono substituted hydrazines and by the steric requirements of the RF group in the 1,3-diketones. Polymethylene chain containing pyrazoles obtained from the 1,3-diketones in question and hydrazine prefer the 3-RF tautomeric form, irrespective of carbocyclic ring size and polyfluoroalkyl group chain length.Key words: polyfluorinated 1,3-diketones, hydrazines, isomeric pyrazoles, molecular structure.
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