BrCCBr.[Mg].Br[C:7]1[CH:11]=[CH:10][S:9][CH:8]=1.[CH3:12][C@H:13]1[CH2:18][C:17](=[O:19])[CH2:16][CH2:15][O:14]1>C(OCC)C>[OH:19][C@:17]1([C:7]2[CH:11]=[CH:10][S:9][CH:8]=2)[CH2:16][CH2:15][O:14][C@@H:13]([CH3:12])[CH2:18]1
A solution of 1,2-dibromoethane (5 g) in diethyl ether (10 ml) was added to a stirred suspension of magnesium (3 g) in diethyl ether (10 ml) to initiate the formation of a Grignard reagent. A mixture of 1,2-dibromoethane (16.7 g) and 3-bromothiophene (4 g) in diethyl ether (30 ml) was added dropwise. The mixture was stirred and heated to reflux for 2 hours. A solution of (2S)-2-methyltetrahydropyran-4-one (2 g) in diethyl ether (5 ml) was added and the mixture was heated to reflux for 1 hour. The mixture was partitioned between ethyl acetate and water. The organic phase was dried (MgSO4) and evaporated. The residue was purified by column chromatography using a 7:3 mixture of petroleum ether and ethyl acetate as eluent. There were thus obtained in turn (2S,4R)-4-hydroxy-2-methyl-4-(3-thienyl)tetrahydropyran (0.685 g, 18.5%) and the corresponding (2S,4S)-isomer (1 g, 32%).
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