Syntheses of Allylketones, α, β-Unsaturated Ketones, and Methylketones from Carboxylic Acids

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Various allylketones were prepared from carboxylic acids and allylmagnesium chloride. For example, the reaction of allylmagnesium chloride with hexanoic acid (1) gave 1-nonen-4-one (2). When these allylketones were treated with various acidic or basic catalysts, they were isomerised to the corresponding α, β-unsaturated ketones or methyl ketones. For example, tans-2-nonen-4-one (4) was obtained by the isomerisation of 1-nonen-4-one (2) with p-toluenesulphonic acid. By treating of 1-nonen-4-one (2) with 3 N sodium hydroxide solution, 2-heptanone (6) was obtained. These ketones can be used as starting materials for the synthesis of terpenes. For example, a new terpenic ketone, 3, 7-dimethyl-1-octen-5-one (10) was obtained from 6-methyl-trans-2-hepten-4-one (9) and vinylma gnesium chloride.