OC[CH2:3][C:4]1[C:9]([OH:10])=[C:8]([O:11][CH3:12])[C:7]([O:13][CH3:14])=[C:6](O)[C:5]=1C.[H-].[Na+].[CH3:19]I.Cl.[CH2:22]([CH2:25][O:26][CH3:27])[O:23][CH3:24]>>[CH3:24][O:23][C:22]1[C:5]([CH2:6][CH2:7][O:13][CH3:14])=[C:4]([CH3:3])[C:9]([O:10][CH3:19])=[C:8]([O:11][CH3:12])[C:25]=1[O:26][CH3:27]6-(2-Hydroxyethyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone (350 mg) which was obtained in Example 3 was treated with sodium hydrosulfite to give 6-(2-hydroxyethyl)-2,3-dimethoxy-5-methylhydroquinone (313 mg). A solution of the hydroquinone (290 mg) in dimethoxyethane (DME, 4 ml) was added dropwise to a suspension of 60% sodium hydride (450 mg) and methyl iodide (2.7 ml) in DME (3 ml) within 90 minutes at 45°-60° C. After cooling, the reaction mixture was treated with diluted hydrochloric acid. The aqueous layer was separated and extracted with ethyl ether. The combined ethereal layer was worked up in the usual manner. The resulting residue (240 mg) was purified by a silica gel column chromatography to give 1,2,3,4-tetramethoxy-5-methyl-6-(2-methoxyethyl)benzene (330 mg). To a solution of this compound (210 mg) in tetrahydrofuran (14 ml), silver (II) oxide (490 mg) and 6N nitric acid (1 ml) were added. After being stirred for 5 minutes at 0° C., silver (II) oxide (2 g) and 6N nitric acid (2 ml) were further added. The reaction mixture was worked up in the usual manner and purified by column chromatography to give 2,3-dimethoxy-5-methyl-6-(2-methoxyethyl)-1,4-benzoquinone as an orange oil. NMR spectrum (δ value in CDCl3): 2.05 (3H, s, CH3 on ring), 2.73 (2H, t, J=6 Hz, CH2 on ring), 3.32 (3H, s, OCH3), 3.47 (2H, t, J=6 Hz, CH2O), 4.00 (6H, s, OCH3 on ring).
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