Electrogenerated Base Induced Dehydrodimerization and Dehydrotrimerization of Pyrazolones

Electrogenerated base induced dehydrocoupling of pyrazol-5-ones was investigated. The results showed that dehydrodimers and dehydrotrimers were generated simultaneously under electrolytic conditions, and their ratio was mainly dependent on the reaction temperature and the nature of the supporting electrolyte. It was observed that the formation of dimer 2 is preferred at lower temperatures and that trimer 3 is preferentially formed at higher temperatures. In addition, higher yields of 3 could be obtained when NaI was used as the supporting electrolyte. The dehydrocoupling reaction of pyrazol-5-ones to form dimer 2 and trimers 3 and 4 was proposed to be through an EGB-induced cascade mechanism.