Phthalazine ring, 1-amino

Polyphosphoric acid (PPA) has recently been used for the intramolecular reaction of a properly positioned amino group with the carbonyl group of the lactam function of a pyridazin-3(2//)-one unit as exemplified by the ring closure of 2-(2-aminophenyl)phthalazin-l(2//)-one <2006T10018>. 

Tautomerism, particularly keto-enol, thione-thiol and amino-imino, was discussed in CHEC-I <84CHEC-l(3B)l>. In general, hydroxy substituents at all positions of the heterocyclic ring of pyridazines, phthalazines, and cinnolines exist in the keto form, with the exception (noted in CHEC-I) of the 3- and 5-hydroxy derivatives of pyridazine 1-oxide. In cases where two hydroxy or thiol substituents are present, the normal situation is for only one to be in the keto or thione form. In contrast, amino derivatives usually exist as such. 

The conversion of primary aminophthalazines into halogenophthalazines (Section 10.1.2), of aminophthalazines into phthalazinones or extranuclear hydro-xyphthalazines (Section 11.1.1 and 11.2.1), of primary phthalazinamines into phthalazinequinones (Section 11.3.1), and of one amino- into another aminophtha-lazine (Section 13.2.1) have been covered already. Other reactions, including some of the ring NH groups in reduced phthalazines, are illustrated in the following classified examples. 

The new fused-ring nitrogen heterocycles perfluorocinnoline, " 5-chloro-pentafluorocinnoline, perfluorophthalazine, and perfluoroquinazoline have been prepared by heating their perchloro-analogues with anhydrous potassium fluoride. All three perfluorinated compounds are extremely susceptible to nucleophilic attack and release fluorine as fluoride ion on exposure to atmospheric moisture. The chemistry of perfluoro-phthalazine and -quinazoline revealed so far is summarized in Schemes 43 and 44, respectively. Perfluorocinnoline reacts rapidly with moist air and aqueous ammonia to yield 4-hydroxy- and 4-amino-pentafluorocinnoline, respectively, and... 

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