The addition of ethylhydrazine to α,β- and β,γ-unsaturated ketones: a quantum-chemical modeling

Abstract

Abstract The reactivity of α,β- and β,γ-unsaturated ketones with respect to the nucleophilic attack by ethylhydrazine in one of the key stages of the formation of 4,5-dihydropyrazole has been studied. It is shown that the addition of the terminal nitrogen atom of ethylhydrazine to the carbonyl group of β,γ- and α,γ-unsaturated ketones with the formation of β,γ- and α,β-unsaturated hydrazones is energetically preferable with the participation of two water molecules. At the same time, the addition of the internal nitrogen of ethylhydrazine to the double C=C bond of the α,β-unsaturated ketone (which is preferable in the presence of one water molecule) to give β-ethylhydrazinyl ketone occurs with a lower activation barrier and is thermodynamically more favorable than the addition to the C=O bond.