The reaction of 1-phenyl-4-vinylpyrazole with diethyl azodicarboxylate. X-Ray molecular structure of 1,2-bisethoxycarbonyl-1-[2-hydroxy-2-(1-phenylpyrazol-4-yl)ethyl]hydrazine

Abstract

1-Phenyl-4-vinylpyrazole does not undergo cycloaddition reactions with alkenes or alkynes, but a dihydro-oxadiazine is formed via a (_π4 +_π2) cycloaddition reaction with diethyl azodicarboxylate under completely anhydrous conditions. In the presence of water the dihydro-oxadiazine undergoes a ready ring-opening reaction to produce a (2-hydroxyethyl)hydrazine derivative, the structure of which was confirmed by X-ray crystallographic analysis. The analysis of a single twin of the chiral crystals showed a disorder ratio of 65 : 35 due to inversion at the chiral C(6) centre.