Ammonium Chloride → 2-(2,5-Dimethoxy-tetrahydrofuran-3-yl-methylidene)-1,3-dithiane

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According to a procedure described in Boger, D. L.; Brotherton, C. E. J. Org. Chem. 1984, 49, 4050-4055, to a solution of 2-trimethylsilyl-1,3-dithiane (1.2 mL, 6.3 mmol) in dry THF (40 mL) at 0° C. was added n-butyllithium (4 mL of 1.6 M in hexanes). After 15 minutes at 0°C. and 20 minutes at 4 mL of 1.6 M ambient temperature, a solution of 2,5-dimethoxytetrahydrofuran-3-carboxaldehyde (1.00 g, 6.00 mmol) in dry THF (10 mL) was added dropwise. After 17 hours at ambient temperature, the resultant mixture was treated with saturated aqueous NH4Cl (10 mL) and partitioned between EtOAc and H2O. The layers were separated and the aqueousueous phase extracted with EtOAc:hex (1:1) two times. The combined organic layers were washed with brine, dried over Na2SO4, and concentrated to afford a residue which was purified via flash column chromatography with 10% EtOAc/hex as eluant to yield 1.06 g (70%) of a mixture of diastereomeric 2-(2,5-dimethoxy-tetrahydrofuran-3-yl-methylidene)-1,3-dithiane as a yellow oil, which was used without any further purification. 1H NMR: δ 6.00 (d, 1H, J=9.6 Hz), 5.93 (d, 1H, J=9.6 Hz), 5.77 (d, 1H, J=9.6 Hz). Anal. Calculated for C11H18O3S2 : C, 50.35; H, 6.92; S, 24.44. Found: C, 50.07; H, 7.00; S, 24.33.

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