1 -Phenyl-1,2-dihydro-1 -phthalazine

Ethyl l//-azepine-l-carboxylate (1) undergoes slow cycloaddition with diethyl diazenedicar-boxylate to give the [4 + 2] 7t-adduct 14 and not, as was first thought, the [6 + 2] 7t-adduct.257 4-Phenyl-l,2-dihydro-l,2,4-triazole-3,5-dione257 258 and phthalazine-1,4-dione257 react likewise. 

Einige 4-substituierte 1-Phenyl-phthalazine werden in 1 n Salzsaure (mit 30—40% Athanol) unter Abspaltung der 4-standigen Substituenten und Ringverengung zu 1-Phenyl-2,3-dihydro-isoindol (70-95% d.Th.) reduziert1 ... 

A combination EIMS and X-ray study of [l,2,4]triazolo[l,2-b]- and [l,3,4]thiadiazolo[3,4-i>]phthalazines was undertaken [95JHC283], and X-ray crystal structure determinations of 5-(2-chlorobenzyl)-6-methyl-3(2W)-pyridazinone [95AX(C)1834], and on 6-benzyloxy-7,8-dihydro-8-phenyl-3-trifluoromethyl-r-triazolo[4,3-i>]pyridazine and its 5,6-dihydro-6-one derivative [95AX(C)1829] have been performed. Structures of some pharmacologically-active pyridazines previously reported as arylidene-4,5-dihydropyridazines need to be revised to those of aromatic pyridazine tautomers 6-8 based on a combination H NMR nOe and X-ray study [95AJC1601],... 

Phthalazine l,4-Dihydroxy-5(or 6)-dimethylamino- E9a, 752 (subst. Phthalanhydrid/N2H4) lH-PyrazoI 5-Methyl-5-nitro-4-phenyl-4,5-dihydro- X/l, 426 Pyrido[2,3-d]pyrimidin 4-Hydroxy-2-oxo-l-propyl-1,2-dihydro- E9c,... 

On the other hand, the diazetidines 5 and 7 only are produced by the reaction of indene with phthalazine-l,4-dione (4)4 and 4-phenyl-3//-l,2,4-triazole-3,5(4//)-dione (6)1. The adduct 7 was successively converted to fra .v-(l,2-dihydro-3-hydroxy-2-indenyl)triazolidinone by acidic hydrolysis T Furthermore, the diazctine was prepared by a sequence involving hydrolysis of the triazolidine ring with concomitant decarboxylation, and oxidation of the intermediate diaze-tidine5. 

The reduction course of substituted phthalazines depends on the substituents thus 1-methylphthalazine is reduced in alkaline solution to l-methyl-3,4-dihydrophthalazine, whereas l-phenyl-4-dimethylaminophthalazine is reduced to 1,2-dihydro-l-phenyl-4-dimethylaminophthalazine. 

Bromo-2-methoxymethyl-6-phenyl-3(277)-pyridazinone (154) with ethyl acrylate gave ethyl 2-methoxymethyl-l-oxo-4-phenyl-l,2-dihydro-6-phthalazine-... 

The conversion of an isoquinoline to a phthalazine is represented by only one example 3-oxo-2-phenyl-2,3-dihydro-1,4-isoquinolinequinone (287) in ethanolic hydrazine hydrate at 20°C during 2h afforded 4-oxo-3 4-dihydro-1-phthalazine-carbohydrazide (288) but in only 9% yield after separation from an isoindolinone the mechanism remains unclear." o... 

Hydrazinocarbonylmethyl-4-phenyl-l(2//)-phthalazinone (84) with triethyl orthoformate gave 2-(5-oxo-2-pyrazolin-4-yl)-4-phenyl-l(2f/)-phthalazinnne. (85) (neat reactants, reflux, 4h 80%), with carbon disulfide/potassium hydroxide gave 2-(3-oxo-5-thioxopyrazolin-4-yl)-4-phenyl-1 (2//)-phthalazi-none (86) (reactants, EtOH, reflux, 4 h 75%), or simply on fusion gave 3,4-dihydro-2H-[l,2,4]triazino[3,4-a]phthalazin-3-one (87) (200°C, 1 h 75%) ° also analogous cyclizations. ° ° ... 

Dimethylamino-2-phenacylphthalazin-2-ium bromide (134) with hydrazine hydrate gave 7-dimethylamino-3-phenyl-l,l lb-dihydro //-[l,2,4]triazino [3,4-fl]phthalazine (135) (EtOH, 20°C, 24 h 95%) also analogous cycliza-... 

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