Synthesis, spectroscopic characterisation and X-ray analysis of regioisomeric 1,3,5-trisubstituted pyrazoles

A new series of regioisomeric 1,3,5-trisubstituted pyrazoles 7–9(a,b) have been synthesized by the reaction of β-diketones (4–6) with methyl hydrazine in ethanol. All the compounds are characterised by the FT-IR, 1H, 13C NMR and mass spectrometry. The crystal structure of compounds 7a, 7b and minor isomer 8b have been determined by X-ray single crystal analysis which showed either of the substituted groups attached to pyrazole ring are essentially non-planar to the central pyrazole ring. Addition of trace amounts of acetic acid during the synthesis of compound 8 resulted in an unexpected compound 10 which is characterised by the X-ray single crystal analysis and is essentially planar. However, crystal structure of 10 is already reported. All structures are further stabilized by the classic and non-classic inter- and intramolecular hydrogen bonding.

► New series of regioisomeric 1,3,5-trisubstituted pyrazoles are synthesized by the reaction of β-diketones with methyl hydrazine.
► All compounds are characterised by FT-IR, NMR and Mass spectrometry.
► Four compounds are further discussed in term of hydrogen bonding by X-ray single crystal analysis.