[CH3:1][CH:2]1[C:10]2[CH:9]=[C:8]3[O:11][CH2:12][C:13](=C)[CH2:14][O:15][C:7]3=[CH:6][C:5]=2[CH2:4][CH2:3]1.I([O-])(=O)(=O)=[O:18].[Na+]>C(#N)C.O.C(Cl)(Cl)(Cl)Cl.O.[Ru](Cl)(Cl)Cl>[CH3:1][CH:2]1[C:10]2[CH:9]=[C:8]3[O:11][CH2:12][C:13](=[O:18])[CH2:14][O:15][C:7]3=[CH:6][C:5]=2[CH2:4][CH2:3]1
6.6 g (30.5 mmol) of 1-methyl-7-methylene-2,3,7,8-tetrahydro-1H,6H-5,9-dioxacyclohepta[f]indene were dissolved in a mixture of 140 ml of acetonitrile, 140 ml of water and 90 ml of carbon tetrachloride. 6.50 g (30.5 mmol) of sodium periodate were added at room temperature with stirring, with the temperature falling to 15° C. After stirring for 30 min, 0.3 g (1.5 mmol, 5 mol %) of ruthenium (III) chloride hydrate were then added, with the temperature increasing back to 30° C. The mixture was stirred for 48 h at room temperature, in the course of which, after 6 h, a further 6.50 g (30.5 mmol) of sodium periodate and 0.3 g (1.5 mmol, 5 mol %) of ruthenium (III) chloride hydrate were added. The reaction mixture was then poured into 500 ml of water and the product was extracted three times, each time with 200 ml of dichloromethane. The combined organic extracts were washed with 200 ml of 20% sodium hydrogen sulfite solution and 200 ml of water and dried over sodium sulfate. After removing the solvent on a rotary evaporator and flash chromatography (pentane/ether, 4:1, Rf=0.32) on silica gel, 3.3 g (50%) of 1-methyl-2,3-dihydro-1H-5,9-dioxacyclohepta[f]inden-7-one (2) were obtained as colorless crystals of m.p. 79-80° C.
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