Imidazole → 6-(10-Acetoxydecyl)-4-tert-butyldiphenylsilyloxy-2,3-dimethoxy-5-methylphenol

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Reaction Steps

2,3-Dimethoxy-6-(10-hydroxydecyl)-5-methylbenzoquinone (3.38 mg, 10 mmol) was dissolved in dichloromethane (50 ml). Pyridine (1 ml) followed by acetyl chloride (0.8 ml) was added with stirring under ice-cooling. The mixture was stirred for 1 hour. Water (50 ml) was added to the reaction mixture which was then stirred for 20 minutes. Then sodium hydrosulfite (4 g) was added, and the mixture was stirred at room temperature for 2 hours. The dichloromethane layer was separated, dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The residue was dissolved in dichloromethane (50 ml), and tert-butylchlorodiphenylsilane (5.5 g, 20 mmol) and imidazole (1.36 g, 20 mmol) were added. The mixture was stirred at 43° C. for 16 hours under a stream of nitrogen. The reaction mixture was washed with water, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to obtain crude 6-(10-acetoxydecyl)-4-tert-butyl diphenylsilyloxy-2,3-dimethoxy-5-methylphenol. The concentrate was dissolved in dichloromethane (100 ml). Triethylamine (2 ml) followed by acetyl chloride (0.8 ml) was added, and the mixture was stirred for 30 minutes. The reaction mixture was washed with water and concentrated under reduced pressure. The residue was dissolved in tetrahydrofuran (50 ml), and tetrabutylammonium fluoride trihydrate (1.3 g, 50 mmol) was added. The mixture was stirred at room temperature for 30 minutes. The reaction mixture was concentrated under reduced pressure, and the residue was dissolved in dichloromethane, washed with water and then dried over anhydrous magnesium sulfate. The dichloromethane layer was concentrated under reduced pressure to obtain crude 1-acetoxy-6-(10-acetoxydecyl)-2,3-dimethoxy-4-hydroxy-5-methylbenzene. This crude product was dissolved in dimethylformamide (15 ml). Sulfur trioxidepyridine complex (6.4 g, 40 mmol) was added, and the mixture was allowed to react for 5 hours at room temperature. The reaction mixture was concentrated under reduced pressure. The residue was dissolved in methanol (40 mi), 1N sodium hydroxide solution (30 ml) was added, and the mixture was stirred at room temperature for 16 hours. The reaction mixture was concentrated under reduced pressure, and the residue was extracted with ether. The aqueous layer was subjected to Amberlite (trade mark) XAD-II column chromatography and eluted with water followed by 50% ethanol/water. The desired fraction was lyophilized to obtain the desired compound (2.4 g).

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