[Br:1][C:2]1[C:3]2[O:19][CH:18]([CH2:20][OH:21])[CH2:17][C:4]=2[C:5]2[O:9][N:8]=[C:7]([C:10]3[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=3)[C:6]=2[CH:16]=1.O.S(=O)(=O)(O)[OH:24]>CC(C)=O.[O-2].[Cr+6].[O-2].[O-2]>[Br:1][C:2]1[C:3]2[O:19][CH:18]([C:20]([OH:24])=[O:21])[CH2:17][C:4]=2[C:5]2[O:9][N:8]=[C:7]([C:10]3[CH:11]=[CH:12][CH:13]=[CH:14][CH:15]=3)[C:6]=2[CH:16]=1
A portion (0.7 g) of the 5-bromo-7,8-dihydro-3-phenylfuro[2,3-g]-1,2-benzisoxazole-7-methanol prepared in Example 4 was dissolved in 50 ml of acetone. To the stirred solution, a mixture of chromium (VI) oxide (1 g), water (3 ml) and concentrated sulfuric acid (1.4 g) was added dropwise over time, and the solution was stirred for 6 hours at room temperature. The insolubles were filtered off by suction. After distilling off the acetone, water was added to the residue and the mixture was subjected to extraction with ether. The ether layer was washed with water and dried. After distilling off the solvent, the residue was recrystallized with acetone-water, yielding 0.4 g of 5-bromo-7,8-dihydro-3-phenylfuro[2,3-g]-1,2-benzisoxazole-7-carboxylic acid. m.p. 241.5°-243.5° C. (with decomposition).
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