[O:1]1[C@H:5]2[O:6][CH2:7][CH2:8][C@H:4]2[C@@H:3]([OH:9])[CH2:2]1.O1[C@H]2OCC[C@H]2[C@H](O)C1.O1[C@@H]2OCC[C@@H]2[C@H](O)C1.O1[C@@H]2OCC[C@@H]2[C@@H](O)C1.P([O-])([O-])(O)=O.[K+].[K+].Cl[O-].[Na+].S([O-])([O-])(=O)=S.[Na+].[Na+].P(=O)(O)(O)O>C(C(C)=O)C.O>[O:1]1[C@H:5]2[O:6][CH2:7][CH2:8][C@H:4]2[C:3](=[O:9])[CH2:2]1
A mixture (287 g, content 69.7%, 1.54 mol) containing (3R,3aS,6aR)-hexahydrofuro[2,3,b]furan-3-ol, (3S,3aS,6aR)-hexahydrofuro[2,3,b]furan-3-ol, (3S,3aR,6aS)-hexahydrofuro[2,3,b]furan-3-ol and (3R,3aR,6aS)-hexahydrofuro[2,3,b]furan-3-ol obtained by the same method as in Example 4 was dissolved in methyl ethyl ketone (2000 ml), and to this was added a solution prepared by dissolving dipotassium hydrogen phosphate (937 g, 5.38 mmol) in water (600 ml). To this was added 2,2,6,6-tetramethylpiperidinyl-1-oxy (1.2 g, 7.7 mmol), and the mixture was cooled to about 0° C. A sodium hypochlorite aqueous solution (1490 g, effective chlorine concentration 13.5%, 2.83 mol) was dropped at 15° C. or less, and the mixture was stirred for 1 hour. After completion of the reaction, a 10% sodium thiosulfate aqueous solution (220 ml) was added and the mixture was stirred for 30 minutes and neutralized with 85% phosphoric acid, and liquid-partitioned. Further, the aqueous layer was extracted twice with methyl ethyl ketone (1000 ml) and the organic layers were combined. To the organic layer was added 1.0 g of hydroquinone, and 3000 ml of the solvent was distilled off. To the concentrated residue was added anhydrous magnesium sulfate (30 g), sodium bicarbonate (20 g) and activated carbon (10 g) and the mixture was stirred for 1 hour. Magnesium sulfate, sodium bicarbonate and activated carbon were filtrated, then, 2-propanol (3000 ml) was added, and the solvent (3300 ml) was distilled off, then, recrystallization was carried out to obtain a white crystal (3aR,6aR)-tetrahydrofuro[2,3-b]furan-3(2H)-one (156.5 g, purity 99.5%, yield 79.1%). At this stage, the enantiomer excess was 100% ee.
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