A Novel Synthesis of 2, 3-Dimethoxy-5-methyl-p-benzoquinone

2, 3-Dimethoxy-5-methyl-p-benzoquinone (3), an important intermediate in the synthesis of ubiquinones (1), was synthesized from 3, 4, 5-trimethoxysalicylic acid (6) or 2, 3, 4-trimethoxybenzaldehyde (9). 6 was reduced via the ethoxycarbonyl derivative (7) to 6-methyl-2, 3, 4-trimethoxyphenol (8) with sodium borohydride, and then 8 was oxidized to 3 in high yield with ferric chloride. On the other hand, 2, 3, 4-trimethoxyphenol (10) was obtained from 9 by the Baeyer-Villiger reaction or treatment with hydrogen peroxide under acidic or basic conditions, and then converted into 8 by reductive methylation. Sodium borohydride reduction of the Mannich base (11) of 10 also gave 8.