[CH2:1]([C:4]1[CH:5]=[C:6]2[C:11](=[C:12]([O:15][CH3:16])[C:13]=1[OH:14])[O:10][C:9](=[O:17])[CH:8]=[C:7]2[CH3:18])[CH:2]=C.O.I([O-])(=O)(=O)=[O:21].[K+]>CO.[Os](=O)(=O)(=O)=O>[OH:21][CH:2]1[O:14][C:13]2=[C:12]([O:15][CH3:16])[C:11]3[O:10][C:9](=[O:17])[CH:8]=[C:7]([CH3:18])[C:6]=3[CH:5]=[C:4]2[CH2:1]1A solution of 2.0 g (8.12 mmols) of 6-allyl-7-hydroxy-8-methoxy-4-methylcoumarin in 20 ml of methanol was treated (mechanical stirring) with 10 ml of water, 5.0 g potassium periodate, and 1.0 ml of a 10% aqueous solution of osmium tetroxide (10 mg/ml). After 3.5 hrs, the mixture was partitioned between water/methylene chloride. The aqueous phase was further extracted with methylene chloride. The organic extracts were dried and evaporated to yield 2-hydroxy-9-methoxy-5-methyl-2,3-dihydro-7H-furo[3,2-g][1]benzopyran-7-one. The compound was dissolved in 40 ml of 98% formic acid and heated under reflux for 1.0 hr. The solution was cooled and evaporated to dryness. The residue was chromatographed over silica, eluting with ethyl acetate/benzene, 1:4, to afford pure 9-methoxy-5-methyl-7H-furo[3,2-g][1]benzopyran-7-one, m.p. 167°-168° (ethanol).
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