Trifluoroacetic Acid

Typical Procedure:
To a stirred solution of alcohol 1 (913 mg, 3.06 mmol) in benzene (85 mL) are added DMSO (1.31 mL, 18.4 mmol), pyridine (0.37 mL, 4.6 mmol), CF₃COOH (0.35 mL, 4.6 mmol), and dicyclohexylcarbodiimide (1.89 g, 9.2 mmol). After being stirred for 30 min, the resulting white solids are filtered off. The filtrate is diluted with AcOEt (500 mL), and this is wshed with H₂O (100 mL). The organic phase is dried over Na₂SO₄ and concentrated in vacuo. To the residue is added a small amount of AcOEt, and the precipitates are filtered off. The filtrate is concentrated in vacuo to give crude tetrahydrofuranone 2, which is reduced directly. The residue is dissolved in MeOH (20 mL), and NaBH₄ (174 mg, 4.6 mmol) is added. After being stirred for 1 h, the mixture is neutralized with Amberlite IR-120 (H⁺). The resin is removed by filtration and washed with MeOH. The combined filtrate and washings are concentrated in vacuo. The residue is purified by flash column chromatography (SiO₂, AcOEt : Toluene = 1 : 20) to give the epi alcohol 3 (758 mg, Y. 83%) as white crystals.