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The substituted pyridazinones 3-phenyl-and 1,3-diphenyl-5-benzylidene-1,4,5,6-tetrahydr~p~ridazinone-6 have been prepared from a-phenacylcinnamic acid hydrazide and a-phenacylcinnamic acid phenylhydrazone, respectively. The dipyridazinone 5,5-di(3-phenyl-1,4,5,6-tetrahydr0)pyridazinone-6 was prepared from the dilactone IV, isolated as a side product in the synthesis of lactone VI.Rearrangement of 4-phenylazo-2-phenyloxazolin-5-one now has been found to proceed also in the presence of acidic reagents.a-Benzylidene-y-phenyi-aP*y-butenolide* (I) has been reported to undergo ring opening upon treatment with aqueous base, with methanol under both acidic and basic conditions (1, 2 ) and with benzylamine (I) t o form a-phenacylcinnamic acid (IIa), its methyl ester (IIb), and its benzylamide derivative (IIe) respectively.This investigation was undertaken with a view to study the behavior of the hetero-ring in compound I toward the action of hydrazines. Treatment of compound I with hydrazine hydrate effected ring opening with the formation of a-phenacylcinnamic acid hydrazide (116). The latter compound underwent ring cIosure upon treatment with hydrochloric acid -acetic acid mixture or with aqueous sodium hydroxide solution with the formation of 3-pl~enyl-5-benzylidene-1,4,5,6-tetrahydropyridazinone-6 (IIIa) (or its tautomer).The proposed structure for the hydrazide IIc finds support from the fact that this compound was readily obtained via treatment of methyl a-phenacylcinnamate (IIb) with *This nomenclature i s after that used by Filler ( 1 ) .

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