Ring-Closure Reaction of Ethyl 4-Hydroxyimino-2-oxovalerate in the Presence of Hydroxylamine

Abstract

Ring-closure reaction of ethyl 4-hydroxyimino-2-oxovalerate [ 1 ], catalyzed by sulfuric acid, brings about isoxazole, and ethyl 3-rnethy1-5-isoxazolecarboxylate (2) is formed in the absence of hydroxylamine. However, in the presence of hydroxylamine, ethyl 5-methyl-3-isoxazolecarboxylate [3 ] and ethyl 3-methyl-5-isoxazolecarboxylate [ 2 ] are formed. The relation between the reaction rate and the sulfuric acid concentration is illustrated in Fig.3. On the basis of the kinetic consideration and the results of analyses of the intermediates formed during the ring-closure reaction, possible pathways for ring-closure of ethyl 4-hydroxyimino-2-oxovalerate in the presence of hydroxylamine were suggested.