The Ring Contraction of Pyridazinones to Pyrazoles. V

Abstract

In order to explore the scope of the ring contraction of pyridazinone to pyrazole, 2-phenyl-3 (2H)-pyridazinones (IIIa-f) and (IVa-e) having 4 and 5 substituents other than chlorine were prepared and examined their behavior against sodium hydroxide. Amongthem, (Ma, b) and (IVa, b, e) undergothe ring contraction to afford the corresponding pyrazole carboxylic acid, (V), (VII), and (VIII). From available data, substituent effects and mechanisms for these ring contractions were discussed.
In the course of this study, an unusual displacement reaction was observed in the reaction of 2-phenyl-4-chloro-5-methylthio-3 (2H)-pyridazinone (IIIa) with sodium hydroxide and sodium ethoxide.