From a Benzene Derivative as Substrate and One Synthon

Oxidation of o-bis(tosylhydrazonomethyl)benzene (23) gave phthalazine (24) [Pb(OAc)4, CH2CI2, 20°C, 2h 81% as its p-toluenesulfonate salt].  

In such a phthalazine synthesis, the synthon could supply Cl, N2, Cl +N2, N2 + N3, C1+N2 + N3, or C1+N2 + N3 + C4. Of these possibilities, the second, third, and last are unrepresented (at least in the literature under review), and of the remaining three categories only that in which the synthon supplies N2 + N3 has been used widely. 

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In much the same way as synthesis of their cinnoUne counterparts (see Chapter 1), the primary synthesis of phthalazines (or hydrophthalazines) may be done by cyclization of benzene (or cyclohexane) derivatives already bearing appropriate substituents, by cyclocondensation of benzene (or cyclohexane) derivatives with acyclic synthons that provide one or more of the ring atoms needed to produce the phthalazine system, by analogous processing of other carbocyclic or pyridazine substrates, or by modification of other heterocycUc substrates in various ways, lypical pre-1972 examples in each category of synthesis may be found from cross-references to Simpson s volume (e.g., H 72) or to Singerman and Patel s volume (e.g., E 333) that appear in some section headings. A variety of pre-and post-1972 syntheses have also been reviewed elsewhere. ... 

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