[OH-].[Na+].S(OC)(O[CH3:7])(=O)=O.[OH:10][C@H:11]1[CH2:16][O:15][CH2:14][C@@H:13]([C:17]([O:19][CH3:20])=[O:18])[CH2:12]1>[Br-].C([N+](CC)(CC)CC)C1C=CC=CC=1.C1(C)C=CC=CC=1.O.C(OCC)(=O)C>[CH3:7][O:10][C@H:11]1[CH2:16][O:15][CH2:14][C@@H:13]([C:17]([O:19][CH3:20])=[O:18])[CH2:12]115 ml of 50% NaOH, 367 mg of benzyltriethylammonium bromide and 0.95 ml of dimethyl sulphate are added to a solution of 1.05 g of methyl (cis)-5-hydroxytetrahydropyran-3-carboxylate in 30 ml of toluene. The two-phase mixture is stirred at room temperature for 18 hours. A further 1 ml of dimethyl sulphate is added. The mixture is stirred at room temperature for a further 6 hours, then diluted with water and ethyl acetate, and stirred at room temperature for 20 minutes. The phases are separated, and the aqueous phase is extracted with ethyl acetate. The combined organic phases are washed with brine, dried with sodium sulphate and evaporated. The crude title compound is identified. by means of the Rf from the residue.
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