1 -Phthalazinone, tautomerism

The term oxyphthalazine is used here to cover compounds such as the tautomeric phthalazinone (1), its nontautomeric 0-methyl (2), and iV-methyl derivatives (3 and 4), the extranuclear hydroxymethylphthalazine (5), the phthalazinequinone (6), the phthalazine A -oxide (7), and related derivatives. 

The tautomerism of these phthalazinones has been studied experimentally in some detail,and some theoretical calculations seem to uphold experimental... 

The halogenolysis of tautomeric phthalazinones has been covered in Section 10.1.1. Other recently used reactions are discussed in the following subsections. 

From the limited number of available examples, it appears that tautomeric phthalazinones undergo (9-acylation under mild conditions but A-acylation under more severe conditions, possibly involving an (9 —> A( rearrangement. Analogous A-arenesulfonations have been reported. ... 

Tautomeric phthalazinones undergo several reductive or oxidative reactions, the most important of which is the production of phthalazinequinones or semiquinones. The following examples illustrate such reactions. 

Several other useful reactions of tautomeric phthalazinones that have been employed in the more recent literature are illustrated by the following classified examples. 

Note The indirect aminolysis of tautomeric phthalazinones may be done via halogeno, alkoxy, thioxo, alkylthio, or other such derivatives. Convenient one-pot syntheses are exemplified here. 

The hydrolysis of such ethers to tautomeric phthalazinones or extranuclear hydroxyphthalazines has been covered in Sections 11.1.1 and 11.2, respectively. Other reactions are illustrated by the following classihed examples. 

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... 

In line with our practice elsewhere [3], these A(XR) values are rounded to the nearest 0.05. Afterwards we go on to set out the regularities in logK that are newly apparent, and speculate on how these may possibly be extrapolated to some nearest-neighbor compounds. It also needs to be pointed out that Eq. (12.1) as it stands is inadequate for coping with two other situations that in which no common cation is present, or may not be and that in which there is more than one. The first is touched on in Section 12.5.3, while the second is exemplified by the complexities attached to the tautomerism of 2-phthalazinone 39 and analyzed in Sections 12.3.6 and 12.4.1. We end with an Overview. 

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