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To a mixed solution of ethyl 8-methyl-1,4-dioxaspiro[4.5]decane-8-carboxylate (7.3 g, 32.0 mmol) in acetonitrile (50 mL) and water (50 mL) was added cerium ammonium nitrate (CAN, 2.11 g, 3.85 mmol). The reaction mixture was heated to 70 °C and stirred for 2 hours. After completion of the reaction, the mixture was cooled to room temperature and partitioned with ethyl acetate (50 mL) and water (50 mL). The aqueous layer was further extracted with ethyl acetate (50 mL x 2). The combined organic layers were washed with saturated brine (50 mL × 2), dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford ethyl 1-methyl-4-oxocyclohexanoate (5 g, 85% yield) as a yellow oil, which was used directly in the subsequent reaction.

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