The cyclization of phenacyl ethylene ketal (pok) hydrazones of glyoxals, benzaldehyde and acetaldehyde to the pyrazoles is described, in the case of the hydrazones of benzaldehyde and acetaldehyde, the corresponding imidazoles are also formed. A mechanism is suggested for the formation of the imidazoles. We recently reported the novel cyclization of phenacyl ethylene ketal hydrazones of arylglyorals (1) to the corresponding 3-aroyl-4-phenyl-1-methylpyrazoles (2) .l The mechanism suggested earlisr' for this cyclization indicated that this process might serve as a general h e 1 h e 4 -3 -2 a ) Ar = C6E5 b) Ar = p-CE3C6E4 c) At = p-BrC6E4 to pyrazoles from suitably constructed aldehyde hydrazones of type and 5 . We now describe Benzene *lC13 -'U + 'tyR h e I he Me 5 s 7 a ) R = Ph, b) R = CE3 fully the results of this investigation and the unusual formation of imidazoles (1) as cogroducts of this reaction. The required I-methyl-1-pekhydrazones (I)' were obtained by Condensation of l-methyl-lpekhydrazine' with benzaldehyde and acetaldehyde. Since the very successful results obtained by cyclization of the arylglyoral hydrazones (1, with 75% sulfuric acid were probably due to the unique structure of the substrates involved (vide infra), it was not surprising that these a ) The abbreviation .poV stands for phenacyl ethylene ketal throughout this paper.