[Br:1][C:2]1[S:3][C:4](Br)=[CH:5][CH:6]=1.C(Br)C.[Mg].[CH3:12][C@H:13]1[CH2:18][C:17](=[O:19])[CH2:16][CH2:15][O:14]1.[Cl-].[NH4+]>C1COCC1.C(OCC)C>[Br:1][C:2]1[S:3][C:4]([C@@:17]2([OH:19])[CH2:16][CH2:15][O:14][C@@H:13]([CH3:12])[CH2:18]2)=[CH:5][CH:6]=1A solution of a mixture of 2,5-dibromothiophene (1.9 g) and ethyl bromide (2.56 g) in THF (6 ml) was added dropwise to a stirred suspension of magnesium (0.29 g) in diethyl ether (3 ml) and the mixture was warmed gently to promote the formation of a Grignard Reagent. The mixture was heated to 40° C. for 1 hour. The mixture was cooled in an ice-bath and a solution of (2S)-2-methyltetrahydropyran-4-one [European Patent Application No. 0385662 (Example 20 thereof); 0.61 g] in THF (5 ml) was added dropwise. The mixture was allowed to warm to ambient temperature and was stirred for 16 hours. The mixture was poured into a saturated aqueous ammonium chloride solution and extracted with ethyl acetate. The organic phase was washed with water and with brine, dried (MgSO4) and evaporated. The residue vas purified by column chromatography using initially methylene chloride and then increasingly polar mixtures of methylene chloride and diethyl ether as eluent. There was thus obtained, as a less polar isomer, (2S,4R)-4-(5-bromothien-2-yl)-4-hydroxy-2-methyltetrahydropyran (0.248 g, 19%) as an oil, having the 2-methyl and 4-hydroxy groups in a trans-relationship.
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