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Synthesis of 4-Hydroxy-5-methyl- and 4-Hydroxy-6-methylcyclohexenones by PdII-Catalyzed Oxidation and Lipase-Catalyzed Hydrolysis

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  • Dedicated to Professor Jan-Erling Bäckvall on the occasion of his 65th birthday

Abstract

A short route for the syntheses of methyl-substituted hydroxycyclohexenones, which are building blocks for various natural products, is presented. Both oxygen atoms were introduced as acetates by a palladium(II)-catalyzed 1,4-addition to a 1,3-diene. The distinction between the two acetoxy groups was achieved by regioselective monohydrolysis with lipase from Candida rugosa, which gave 1-acetoxy-4-hydroxy-5-methylcyclohexene and its 6-methyl regioisomer as a separable mixture. The target compounds 4-hydroxy-5-methylcyclohex-2-enone and 4-hydroxy-6-methylcyclohex-2-enone could then be obtained as diastereomeric mixtures in good overall yields and with moderate enantiomeric excesses (31–67 %).

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