Acid-Catalysed Benzophenone Isomerisation

Treatment of 6-carboxy-5 -chloro-2 -hydroxy-2-methylbenzophenone with concentrated sulfuric acid gives, after quenching of the reaction mixture with water, an almost quantitative yield of 2-carboxy-5 -chloro-2 -hydroxy-3-methylbenzophenone. 

Attempts were made to epoxidise the C=C bond of diphenylcyclopropenone and thus obtain the 2-oxabicyclo[1.1.0]butanone derivative. Use of either peracetic acid or hypochlorite was not successful and the starting material was recovered. Oxidation with 25% hydrogen peroxide in a mixture of dioxane and 3M aqueous NaOH at room temperature, however, gave a 77% yield of desoxybenzoin. 

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When 2-methyleneindolines (Fischer s bases) are used as the nucleophilic species, 2-spiroannulated indolines result with high diastereomeric purity (95JPR368). When R1 = Ph, an acid catalysed isomerisation leads to a highly substituted benzophenone (23). 

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