[CH3:1][O:2][C:3]([CH:5]1[CH2:9][CH2:8][C:7]2([CH2:14][CH2:13][CH2:12][CH2:11][CH2:10]2)[CH:6]1[O:15][Si](CC)(CC)CC)=[O:4].[F-].C([N+](CCCC)(CCCC)CCCC)CCC.[Cl-].[NH4+]>O1CCCC1>[CH3:1][O:2][C:3]([CH:5]1[CH2:9][CH2:8][C:7]2([CH2:10][CH2:11][CH2:12][CH2:13][CH2:14]2)[CH:6]1[OH:15])=[O:4]To a solution of 1-triethylsiloxy-spiro[4.5]decane-2-carboxylic acid methyl ester (5.0 g) obtained in Step 2 in tetrahydrofuran (30 mL) was added a 1M tetrahydrofuran solution of tetra-n-butylammonium fluoride (18.4 mL), followed by stirring the reaction mixture at room temperature for 30 minutes. Then, after addition of aqueous ammonium chloride solution, the reaction mixture was extracted with ethyl acetate. The organic layer was washed with water, dried and concentrated. The residue was purified by column chromatography on silica gel (hexane:ethyl acetate (volume ratio)=5:1) to give 1-hydroxy-spiro[4.5]decane-2-carboxylic acid methyl ester (less-polar isomer; 1.6 g, more-polar isomer; 0.95 g).
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