O-Aroylbenzoic acids

Aroylation of an aromatic system by reaction with phthalic anhydride under Friedel-Crafts conditions yields the o-aroylbenzoic acid. These readily available compounds have characteristic melting points which make them useful as derivatives in the characterisation of aromatic hydrocarbons and of aryl halides (Section 9.6.3, p. 1238). 

The aroylation of an aromatic system by reaction with phthalic anhydride under Friedel-Crafts conditions is described in Section 6.11.1, p. 1006. The cyclisation of the derived o-aroylbenzoic acid with polyphosphoric acid is a convenient route to substituted anthraquinones. The reaction is illustrated by the formation of 2-methylanthraquinone from o-(p-toluoyl)benzoic acid (Expt 6.132). 

The intramolecular condensation of o-aroylbenzoic acids in the presence of concentrated sulfuric acid gives substituted anthraquinones. The acid strength, reaction temperature, and period of heating are carefully controlled to insure optimum yields and to avoid sulfonation products. Boric acid has been added as a sulfonation inhibitor. Substitution in the para position of the aroyl group leads to 2-alkyl-, 2-chloro-, and 2-bromo-anthraquinones. ... 

Access to the pharmacologically useful hexahydro-2,5-diazocines (see Section V) has been provided by reductive ring opening of imidazoisoindolones. Sulkowski and co-workers, in most of such reports, reacted o-aroylbenzoic acids with 1,2-diamines, producing compounds 46. These latter compounds were reduced with lithium aluminum hydride, aflbrding diazocines 47... 

J. W. Cook introduced the method of cyclizing an o-aroylbenzoic acid to an anthraquinone by heating the keto acid with phosphorus pentoxide in nitrobenzene at 150-165 . For example, the isomeric acids (3) and (4) resulting from the Friedel-Crafts reaction of 1,2-naphthalic anhydride with thiophene are cyclized to the same quinone (5). ... 

The coupling of o-aroylbenzoic or nicotinic acids with phosphorylated amines using dicyclohexylcarbodiimide (DCC)/4-dimethylaminopyridine (DMAP) followed by deprotonation with potassium bis(trimethylsilylamide) and cyclization gave isoquinolines or naphthyridinones in good yields (Scheme 43) <1996T4433>. 

With benzene the product is o-benzoylbenzoic acid (Expt 6.124), and with toluene, o-(p-toluoyl)benzoic acid (Expt 6.132). The aroylbenzoic acids are important starting materials for the synthesis of quinones (Section 6.11.3, p. 1022), into which they are cyclised using polyphosphoric acid (Expt 6.132). 

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