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

Abstract

The reactivity of 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 unsaturated ketones with the formation of and 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 unsaturated ketone (which is preferable in the presence of one water molecule) to give ethylhydrazinyl ketone occurs with a lower activation barrier and is thermodynamically more favorable than the addition to the C=O bond.