DOI: 10.1016/j.tet.2021.132413

The mechanism of the reaction of hydrazines with α,β-unsaturated carbonyl compounds to afford hydrazones and 2-pyrazolines (4,5-dihydro-1H-pyrazoles): Experimental and theoretical results

The reaction of hydrazines with α,β-unsaturated carbonyl compounds to afford 2-pyrazolines was studied using a dissymmetric chalcone (phenyl/p-tolyl) and three hydrazines, hydrazine itself, phenylhydrazine and thiosemicarbazide. Several products were identified, and some reaction paths established thanks to the evolution of 1H and 13C NMR spectra with time. Theoretical calculations on energies and chemical shifts were of paramount importance to ascertain the structure of some products. For important steps, the transition states were calculated while IRCs proved necessary to find some unexpected intermediates.