7- Hydroxy-6 -phthalazinone, alkylation

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. 

Phthalazin-1 (2H)-one, 4-hydroxy-2-methyl-methylation, 3, 17 Phthalazin-l(2H)-one, 4-methoxy-methylation, 3, 17 Phthalazinones in thermography, 1, 392 Phthalazin-l(2H)-ones alkylation, 3, 17 reaction... 

Competition between the two carboxy residues in the cyclization of alkyl 1,3-dihydro-l-hydroxy-a,a-disubstituted-3-oxo-l-benzoisofuranacetates with hydrazines can lead to phthalazinones and/or pyrazolones (Equation (39)). With ethyl esters a mixture of both products may be obtained, and while increased bulk at the a-position leads to the pyrazolone as the sole product, phthalazinones are the exclusive products from /-butyl esters <9lJOC2587). 

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See also in sourсe #XX -- [ ]

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