[OH:1][C@@H:2]1[CH2:11][C:6]2([CH2:10][CH2:9][CH2:8][CH2:7]2)[C@@H:5]([C:12]([OH:14])=[O:13])[C:4]([CH3:15])=[CH:3]1.[C:16](=O)([O-])[O-].[K+].[K+].CI.Cl>CN(C=O)C>[OH:1][C@@H:2]1[CH2:11][C:6]2([CH2:7][CH2:8][CH2:9][CH2:10]2)[C@@H:5]([C:12]([O:14][CH3:16])=[O:13])[C:4]([CH3:15])=[CH:3]1At 5° C., a solution of the crude trans-9-hydroxy-7-methylspiro[4.5]dec-7-ene-6-carboxylic acid obtained (22.7 g) in DMF (150 ml) was treated with potassium carbonate (16.3 g, 118 mmol) and stirred for 30 min. The resulting mixture was then treated within 6 min. with methyl iodide (13.4 ml, 215 mmol), stirred for 2 h at 20° C., poured into cold 2N aqueous HCl (200 ml), and extracted twice with hexane (150 ml). The combined organic phases were washed with water (100 ml), with a saturated aqueous solution of NaCl (150 ml), dried (MgSO4), and concentrated, giving crude trans-methyl 9-hydroxy-7-methylspiro[4.5]dec-7-ene-6-carboxylate (12.85 g, 36%).
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