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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 chromatograpy with 10% EtOAc/hex as eluant to yield 1.06g (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.

1. waitAfter 17 hours at ambient temperature
2. custompartitioned between EtOAc and H2O
3. customThe layers were separated
4. extractionthe aqueousueous phase extracted with EtOAc
5. washThe combined organic layers were washed with brine
6. dry with materialdried over Na2SO4
7. concentrationconcentrated
8. customto afford a residue which
9. customwas purified via flash column chromatograpy with 10% EtOAc/hex as eluant