Pyrazolidine derivatives from the condensation reaction of hydrazobenzene with aliphatic aldehydes

The condensation reaction of hydrazobenzene with ethanal yields products of the pyrazolidine structure, III or V, according to whether it is carried out in the absence or presence of alcohols, respectively. Propanal reacts similarly to VIII while no reaction could be achieved with butanal. The structural evidence is based mainly on the mass and 1H NMR spectra which disprove the structures IV and VI, originally suggested by Rassow. The reaction is analogous to the condensation of aliphatic aldehydes with N-phenylhydroxylamine yielding 1,2-oxazolidine derivatives VII.