Scope and Limitations in the Regioselective Synthesis of 1,3,5-Trisubstituted Pyrazoles from b-Amino Enones and Hydrazine Derivatives. 13C-Chemical Shift Prediction Rules for 1,3,5-Trisubstituted Pyrazoles

Abstract

β-Amino enones react with hydrazine derivatives to give regioselectively 1,3,5-trisubstituted pyrazoles.The synthetic method only presents limitations when the β-substituent of the enone and the hydrazine substituent are bulky or possess an electron withdrawing character.Comparison of the 13 C-NMR spectra of the seventy pyrazoles allowed us to estimate a 13 C-chemical shift prediction rule for 1,3,5-trisubstituted pyrazoles, with deviations of less than ± 1 ppm.