[Si:1]([O:8][CH2:9][CH:10]([OH:21])[C:11]1[CH:16]=[CH:15][C:14]([C:17]([CH3:20])([CH3:19])[CH3:18])=[CH:13][CH:12]=1)([C:4]([CH3:7])([CH3:6])[CH3:5])([CH3:3])[CH3:2].[O:22]1[CH:27]=[CH:26][CH2:25][CH2:24][CH2:23]1.C1(C)C(S(O)(=O)=O)=CC=CC=1>ClCCl>[Si:1]([O:8][CH2:9][CH:10]([O:21][CH:23]1[CH2:24][CH2:25][CH2:26][CH2:27][O:22]1)[C:11]1[CH:16]=[CH:15][C:14]([C:17]([CH3:20])([CH3:19])[CH3:18])=[CH:13][CH:12]=1)([C:4]([CH3:7])([CH3:6])[CH3:5])([CH3:3])[CH3:2]1-Tert-butyldimethylsilyloxy-2-hydroxy-2-(4-tert-butylphenyl) ethane (0.5 g, 1.622 mmol) is dissolved in dichloromethane and to it is added dihydropyran (0.163 g,1.94 mmol) and toluenesulfonic acid (33 mg, 0.194 mmol). The reaction is stirred for 2 hours after which the mixture is washed with water and dried. The crude residue obtained after concentration is purified by flash chromatography (silica gel; ethyl acetate/hexanes) to obtain the product.
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