Ammonium Chloride → (2R,5S)-2-Isopropyl-3,6-dimethoxy-5-(4,4,4-trifluoro-3-phenyl-butyl)-2,5-dihydro-pyrazine

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A solution of (R)-(−)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine (1.1 g) in tetrahydrofuran (25 ml) was cooled to −70° C., then tert.butyllithium (1.7 M in pentane, 3.88 ml) was added and the mixture was stirred for 1 hour. A solution of (3-iodo-1-trifluoromethyl-propyl)-benzene (1.98 g) in tetrahydrofuran (7 ml) was added slowly and the mixture was stirred overnight at −70° C. At room temperature saturated ammonium chloride solution was added and the mixture was extracted three times with ether. The combined organic layers were dried (MgSO4), filtered and evaporated. The residue was purified by column chromatography (SiO2, heptane/EtOAc=9:1 to yield a yellow liquid, (1.86 g, 83%).

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