Quinones from aromatic diols

Reactions of aldehydes and their derivatives have been the subject of several reports. Benzene-1,2-dicarboxaldehyde condenses" with 2,3-dihydro-naphthazarone to give the p-quinone (75), and a similar reaction occurs between diketones such as PhCOCH2CH2COPh and naphthalene-1,4-diol. 4-Nitrobenzaldehyde undergoes disproportionation in the presence of cyanide ions and methanol, resulting in methyl 4-nitrobenzoate as the main product. The acid-catalysed rearrangement of arylhydrazones (76) derived from aromatic aldehydes and diaryl ketones leads to amino-biphenyls (77). 

N03)j, a newcomer to the arena of oxidants, is useful for the acetoxylation of aromatic side chains in benzylic positions [415, 416] and for the oxidation of methylene or methyl groups that are adjacent to aromatic rings to carbonyl groups [238, 415, 417]. The reagent also oxidizes alcohols to aldehydes [418, 419, 420, 421] and phenols to quinones [422, 423], cleaves vicinal diols to ketones and a-hydroxy ketones to acids [424, 425], and converts diaryl sulfides into sulfoxides [426]. A specialty of ammonium cerium nitrate is the oxidative recovery of carbonyl compounds from their oximes and semicarbazones [422, 427] and of carboxylic acids from their hydrazides [428] under mild conditions. 

The dione (Scheme 22) reacts photochemically with aromatic aldehydes in processes similar to the reactions between quinones and aldehydes. Irradiation of the diketone (343) leads to the formation of the remarkable diol (344). The structure of this product was verified by T-ray analysis. The reaction, brought about by irradiation through Pyrex in various solvents, proceeds via the intermediate keto alcohol (345), a compound isolated at shorter reaction times. There is some doubt in the minds of the authors as to whether the reaction arises by hydrogen abstraction from the y- or the s-positioh. They propose that if the former occurs then the rearrangement by hydrogen migration to yield (I) is kinetically favoured. 

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