Competitive Michael and carbonyl addition of hydrazines to 4-Benzylidene-2-phenyloxazol-5(4H)-one: Synthesis of some new Pyrazolidin-3-ones

Abstract

2-Aryl- and -heteroaryl-4-benzamido-5-phenylpyrazolidin-3-ones (8), (10), (12a), (12b), (14a) and (14b) were prepared by the action of the respective hydrazines on 4-benzylidene-2-phenyloxazol-5(4H)-one (1) in refluxing ethanol. The coproducts formed in lower yields were the isomeric cyclic products (9), (11) and (13), tentatively formulated as 1-substituted pyrazolidin-3-ones and the corresponding hydrazides (3)- (6) of α-benzamidocinnamic acid. However, phenylhydrazine produced more of the hydrazide than of the 4-benzamido-2,5-diphenylpyrazolidin-3-one (3). When the reaction was carried out in refluxing benzene, the major product was the hydrazide irrespective of the hydrazine used. It is concluded that pyrazolidin-3-ones were formed by an initial Michael addition of hydrazine to the benzylidene carbon of the azlactone (1) followed by a cyclization which involves an opening of the azlactone ring.