[OH-].[Na+].[OH:3][C:4]1[C:9]2[C:10](=[O:13])[CH2:11][O:12][C:8]=2[CH:7]=[C:6]([OH:14])[CH:5]=1.[CH2:15](Br)[CH:16]=[C:17]([CH3:19])[CH3:18]>CO>[OH:3][C:4]1[C:9]2[C:10](=[O:13])[CH2:11][O:12][C:8]=2[CH:7]=[C:6]([OH:14])[C:5]=1[CH2:15][CH:16]=[C:17]([CH3:19])[CH3:18].[OH:3][C:4]1[C:9]2[C:10](=[O:13])[CH2:11][O:12][C:8]=2[CH:7]=[C:6]([OH:14])[CH:5]=1
Aqueous sodium hydroxide (20% w/v)) (10 ml) was added to a stirred solution of 4,6-dihydroxy-3-benzofuranone (3 g, 18.1 mmol) in methanol (50 ml), the reaction mixture immediately turned to a brown color. Prenyl bromide (2.1 ml, 18.2 mmol) in methanol (10 ml) was added dropwise to the solution. After stirring for 30 minutes at room temperature, methanol was removed in vacuo, and ethyl acetate (200 ml) was added to the reaction mixture. The aqueous layer was acidified by adding dilute hydrochloric acid (1M, 50 ml). The organic layer was washed with brine, dried over magnesium sulfate, filtered and concentrated in vacuo to give the crude product mixture as a yellow foam. Silica gel chromatography eluting with a mixture of ethyl acetate and hexanes (1:2), gave 4,6-dihydroxy-5-prenyl-3-benzofuranone (1.25 g, 29.5%), unreacted 4,6-dihydroxy-3-benzofuranone (0.7 g, 23.3%) and a mixture of unidentified products (1.1 g) (could be a mixture of 4,6-dihydroxy-2-prenyl 3-benzofuranone and 4,6-dihydroxy-2,2-diprenyl-3 -benzofuranone).
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