Ring closure reactions involving 1‐hydrazinophthalazine. Reactions with 1,2,4‐tricarbonyl and 1,3‐dicarbonyl compounds

Annelation reactions of six‐membered rings to 1‐hydrazinophthalazine, 1, were investigated. With aroyl‐(acyl)pyruvates, 2, the desired system was obtained. It was found that the course of the reaction depends on the reaction condition as well as the substituted pyruvates. Thus, 3‐(2‐oxo‐2‐substituted ethyl)‐4H‐as‐triazino‐[3,4‐a]phthalazin‐4‐one, 4, was the product when 1 reacted with 2 in alcoholic medium. The side chain tauto‐merism of 4 was studied by using ir, 1H‐nmr, and ms spectral methods. When 1 hydrochloride instead of 1 was reacted with 2, 3‐ethoxycarbonyl‐s‐triazolo[3,4‐a]phthalazine, 6, was the major product. The reaction of 1 with benzoylacetone in ethanol afforded the hydrazalone, 9. By ir, 1H‐nmr, and 13C‐nmr methods it was shown that in solution it is inolved in an enhydrazine‐hydrazone as well as a ring‐chain tautomerism. Compound 9 upon the action of PPA underwent dehydrative cyclization to 3‐methyl‐s‐triazolo[3,4‐a]phthalazine, 10, and 3‐methyl‐5‐phenyl‐1‐(l‐phthalazinyl)pyrazole, 7. The reaction of 1 with ethyl phenylpropiolate in ethanol was reported by others to give 1‐(1‐phthalazinyl)‐3‐phenyl‐5‐pyrazolone, 8. Upon reinvestigation of this reaction it is shown that the product actually is ethyl β‐(1‐phthalazinylhydrazono)benzenepropanoate, 11. Attempts to synthesize 8 were unsuccessful by this method. In the reaction of 1 with ethyl benzoylacetate the expected hydralazone 11 was easily formed which upon reaction with PPA yielded the desired species 8.