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Intramolecular Friedel–Crafts acylation of β-9-anthrylpropionic acid gives 1,2-dihydrobenz[de]anthracen-3-one (II) in agreement with earlier work. This product is readily converted into derivatives of the tautomeric 3-hydroxy-7H-benz[de]anthracene (VI; R = OH) and oxidised to the somewhat unstable benz[de]anthracen-3-one (IV). 1,2,7,8-Tetrahydroperylene-3,9-dione (IX), obtained by cyclisation of ββ′-9,10-anthryldipropionic acid, is also readily oxidised; on acetylation it forms 3,9-diacetoxyperylene, a product previously formulated as a dienol acetate. Spectroscopic comparison of the cyclic ketones (IX) and (II) with their acyclic analogues, 1,5-diacetyl- and 1-acetyl-anthracene respectively, indicates considerable difference between the two series in the preferred orientation of carbonyl groups with respect to the anthracene system.

Acylation of 2,6-dimethoxyanthracene with crotonoyl (but-2-enoyl) chloride leads to the formationof the corresponding 1,5-diacyl derivative. This compound, on further treatment with aluminium chloride or polyphosphoric acid undergoes intramolecular O-alkylation with fission of the methoxyl groups and formation of chromanone-type systems. Intramolecular C-alkylation which, alternatively, would have led to a perylene derivative, does not occur. A somewhat analogous sequence of reactions is observed when o-chlorobenzoic anhydride is used as acylating agent. The resulting 1,5-bischlorobenzoyl product in this case undergoes cyclisation at oxygen to yield a dixanthone derivative.

Solutions of 2,6,9-trimethoxyanthracene undergo rapid and quantitative photo-oxidation to 2,6-dimethoxy-9,10-anthraquinone in normal laboratory daylight. Reduction of this quinone with cyclohexyl toluene-p-sulphonate in the presence of zinc gives a mixture of the corresponding anthracene and 2,2′,6,6′-tetramethoxy-9,9′-bianthryl. Aerial oxidation of 2,6-dimethoxyanthrone in basic media results in formation of the anthraquinone together with the 9,9′-dianthraquinone (V) and other further cyclised quinones (VI) and (VII). These reactions are accompanied by novel oxidative demethylation giving 2-hydroxy-6-methoxyanthraquinone.

2-Methyl- and 2,5-dimethyl-NN′-dibenzenesulphonyl-1,4-benzoquinone di-imines undergo side-chain amination by piperidine or piperazine, a process that has analogy in the quinone series. Geometrical isomerism in several of these di-imines is discussed on the basis of n.m.r. spectroscopic evidence. Certain of the nuclear aminated di-imine derivatives are converted photochemically into benzimidazole derivatives. The scope of this novel process is investigated.

Bromination of 2,6-dihydroxyanthracene in acetic acid occurs at the 1,5-positions. Its dimethyl ether, treated similarly, gives a mixture of 1,5- and 9,10-dibromo-derivatives, while its diacetate undergoes 9,10-disubstitution exclusively. 9,10-Dichlorination of the system is similarly effected. Under these conditions the use of 1 mol. of halogen leads to substitution at the 9-position only. The position of halogenation is readily determined by a combination of spectroscopic analysis and oxidation to anthraquinones. The latter process is brought about also by an excess of halogen.

Two-step acylation of 2,6-dimethoxyanthracene with acetyl chloride followed by crotonoyl chloride leads successively to the corresponding 1-acetyl- and 1-acetyl-5-crotonoyl derivatives. Acylation at the 9-position requires an indirect procedure; e.g., 9-formylation is effected by the action of dimethylformamide on the corresponding lithio-derivative. 2,6-Dimethoxy-9-anthraldehyde, so obtained, is relatively unstable and readily converted into 2,6-dimethoxyanthraquinone.

The stereochemistry of dihydropyran aldehydes obtained from the acid-catalysed dimerisation of crotonaldehyde is discussed. Spectroscopic evidence for its re-assignment is presented, based on examination of the corresponding acids.