2- Acetyl-4- phthalazinone

When large groups, such as phenyl, bromo, ethoxycarbonyl or nitro are attached at position 3, the principal products are l-alkylcinnolin-4(l/f)-ones. Cyanoethylation and acetylation of cinnolin-4(l/f)-one takes place exclusively at N-1. Phthalazin-l(2/f)-ones give 2-substituted derivatives on alkylation and acylation. Alkylation of 4-hydroxyphthala2in-l(2/f)-one with an equimolar amount of primary halide in the presence of a base leads to 2-alkyl-4-hydroxyphthalazin-l(2/f)-one and further alkylation results in the formation of 4-alkoxy-2-alkylphthalazinone. Methylation of 4-hydroxy-2-methyl-phthalazinone with dimethyl sulfate in aqueous alkali gives a mixture of 4-methoxy-2-methylphthalazin-l(2/f)-one and 2,3-dimethylphthalazine-l,4(2//,3//)-dione, whereas methylation of 4-methoxyphthalazin-l(2/f)-one under similar conditions affords only 4-methoxy-2-methylphthalazinone. 

Nitration of 4-hydroxymethyl-l(2//)-phthalazinone and its derivative EG-626 with acetyl nitrate has been shown to give, after formation of the methyl nitrate esters, the N-2-nitro derivatives (Scheme 54). An earlier suggestion that the second nitration of EG-626 occurred on the phthal-azinone oxygen was disproved by a combination of spectroscopic methods and an x-ray structure determination <92CPB3327>. 

Acetyl-2-chlorocycloheptatrien-l-one (136) or the isomeric substrate, 2-acetyl-7-chlorocycloheptatrien-l-one (138), underwent condensation and rearrangement with hydrazine to give 4-methyl-l(27/)-phthalazinone (137) (H2NNH2 H2O, MeOH, reflux, 2h 29 or %, respectively) substrate (138) with methylhydrazine gave 2,4-dimethyl-l(2fl)-phthalazinone (139) (MeOH,... 

Biphenyl-4-yl)-l(2fl)-phthalazinone (66) gave a mixture of l-acetoxy-4-(biphenyl-4-yl)phthalazine (67) and 2-acetyl-4-(biphenyM-yl)-l(27/)-phtha-lazinone (68) (AC2O, AcOH), ... 

Hydroxymethyl-l,7(27/,3//)-phthalazinedione (137) apparently underwent acetylation to afford 7-acetoxy-4-acetoxymethyl-l(2fl)-phthalazinone (138) (for details, see original). 

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