A New Synthesis of Methyl Heptenone

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6-Methyl-6 (or 5)-hepten-2-one was synthesized from the addition compounds which were prepared from 4-methyl-l-penten-3-ol acetate or 2-methyl-4-penten-2-ol acetate and acetaldehyde by the Prins Reaction.These addition compounds weve at first hydrolysed to sec- or test-keto-alcohols respectively and then dehydrated to methyl heptenone under appropriate conditions in good yield. The dehydration of 6-methyl-5-hydroxy-2-heptanone was best carried out at 280-370°c by passing through a pyrex glass tube, packed with pumice catalyst containing phosphoric acid. 6-Methyl-6-hydroxy-2-hepta-none was dehydrated to 6-methyl-5-hepten-2-one with a trace of iodine. On the other hand, 6-methyl-6-hydroxy-2-heptanone acetate was subjected to pyrolysis at 450°c through a pyrex glass tube, filled with crushed glass in almost quantitative yield, giving 6-methyl-6-hepten-2-one. 6-Methyl-6-hydroxy-2-heptanone, reported by Verley in 1897, which was obtained by the hydration of methyl heptenone with 40-50% H2SO4, differed apparently from the hydrolygate of 6-methyl-6-hydroxy-2-heptanone acetate. The substance which was obtained by Verley's method, was supposed to be 2, 2-dimethyl-6-methyl-6-hydroxy-tetrahydro pyran. When 6-methyl-5-hydroxy-2-heptanone acetate was hydrolyged with alcoholic sodium hydroxide solution, 2-isopropyl-5-methyl-5-ethoxy-tetrahydrof uran and 6-methyl-5-hydroxy-2-heptanone were obtained. The f uran ring of the former could be opened easily to the latter keto-alcohol when it was boiled with dil. HCl.
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A New Synthesis of Methyl Heptenone

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