[C:1]([O:6][CH2:7][CH3:8])(=[O:5])[C@H:2]([CH3:4])[OH:3].C1(C)C=CC(S(O)(=O)=O)=CC=1.[O:20]1[CH:25]=[CH:24][CH2:23][CH2:22][CH2:21]1.C(=O)([O-])O.[Na+]>ClCCl>[O:20]1[CH2:25][CH2:24][CH2:23][CH2:22][CH:21]1[O:3][C@@H:2]([CH3:4])[C:1]([O:6][CH2:7][CH3:8])=[O:5]In dichloromethane (200 ml) was dissolved (S)-(-)-ethyl lactate (35.4 g), to which was added, under ice-cooling, p-toluenesulfonic acid.hydrate (570 mg). To the mixture was added dropwise 3,4-dihyro-2H-pyran (30.2 g), taking 30 minutes, followed by stirring for one hour under ice-cooling. To the reaction mixture was added a 5% aqueous solution of sodium hydrogen carbonate (50 ml), which was vigorously stirred, then the organic layer was separated. The organic layer was further washed with a 5% aqueous solution of sodium hydrogen carbonate and dried over anhydrous magnesium sulfate, then the solvent was distilled off under reduced pressure to afford ethyl(2S)-2-(3,4,5,6-tetrahydro-2H-pyran-2-yloxy)propionate (61 g) as a pale yellow oily product.
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