[CH3:1][C:2]1([CH3:12])[O:6][C@H:5]2[CH2:7][S:8][C@H:9]([CH:10]=[O:11])[C@H]2O1.[Cr](O[Cr]([O-])(=O)=O)([O-])(=O)=O.[NH+]1C=CC=CC=1.[NH+]1C=CC=CC=1.S([O:39][CH3:40])(OC)(=O)=O.[C:41](=O)([O-])[O-:42].[K+].[K+]>CN(C)C=O.CC(C)=O.O>[CH3:41][O:42][C:10]([C@@H:9]1[C@@H:40]2[C@@H:5]([O:6][C:2]([CH3:1])([CH3:12])[O:39]2)[CH2:7][S:8]1)=[O:11]
2.8 g (0.015 mol) of (3aS,4S,6aR)-2,2-dimethyltetrahydrothieno[3,4-d][1,3]dioxole-4–Carbaldehyde from the aforementioned Experimental Example 6 were dissolved in 200 mL of anhydrous N,N-dimethylformamide to which 26.7 g (0.070 mol) of pyridinium dichromate was added. The reaction mixture was stirred at ambient temperature for 20 h. After 0.3 L of water were added, it was extracted with 2.5 L of ethyl acetate (0.5 L×5). The extract was dried, filtered, and concentrated under reduced pressure to obtain the concentrate which was (3aS,4S,6aR)-2,2-dimethyltetrahydrothieno[3,4-d][1,3]dioxole-4-carboxylic acid. The concentrate was dissolved in 65 mL of acetone to which 2 mL (21.14 mmol) of dimethyl sulfate and 1.2 g (8.68 mmol) of potassium carbonate were added. The resulting mixture was stirred for 2 h. Acetone was distilled off under reduced pressure, and the residue was dissolved in ethyl acetate, followed by washing with water and saturated saline solution. The organic layer was dried and filtered, and the filtrate was concentrated under reduced pressure. The concentrate was purified by silica gel column chromatography using the eluant (hexane:ethyl acetate=3:1) mixture to obtain 2.5 g (yield: 78%) of (3aS,4S,6aR)-2,2-dimethyltetrahydrothieno[3,4-d][1,3]dioxole-4-carboxylic acid methyl ester as an oil.
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