Preparation of Nontautomeric Phthalazinones and Phthalaziniumolates

Most such compounds have been made by primary synthesis (see Chapter 8), by ozonolysis of alkenylphthalazines (see Section 9.2.2), or by alkylation or acylation of tautomeric phthalazinones (see Section 11.1.2.1). Minor preparative routes are 

4-Phenylphthalazin-2-ium-2-benzimidate (211) underwent ring fission, aerial oxidation, and recyclization in alkali to give 2-benzamido-4-phenyl-l(2//)-phthalazinone (212) (KOH, EtOH, HjO, reflux, 3 h 49%).  

2-Methylphthalazin-2-ium-4-olate (213) underwent photolytic rearrangement in water, probably via the bridged intermediate (214), to give 2-methyl-1(2//)-phthalazinone (215) (HjO, 20°C, hv, 10 h 90%).  

4-Diphenyl-1,2-dihydro-l-phthalazinol (216) gave 2,4-diphenyl-l(2//)-phtha  

4-Imino-3-methyl-3,4-dihydro-l-phthalazinamine (217, X = NH) underwent hydrolysis to 4-amino-2-methyl-l(2//)-phthalazinone (217, X = 0) (hot HjO %).  

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