[CH3:1][C:2]1[CH:8]=[CH:7][CH:6]=[C:4]([OH:5])[C:3]=1[OH:9].C(=O)([O-])[O-].[K+].[K+].Br[CH2:17][CH2:18]Br>CN(C)C=O>[CH3:1][C:2]1[C:3]2[O:9][CH2:18][CH2:17][O:5][C:4]=2[CH:6]=[CH:7][CH:8]=1In 300 ml of dry dimethylformamide, was dissolved 30 g of 3-methylcatechol and then 100 g of potassium carbonate was added to the solution. This solution was heated to 120 to 130° C. and 136 g of 1,2-dibromoethane was added dropwise in ten and several portions. After stirring for 30 minutes under the same conditions, the mixture was cooled and solid materials were removed by filtration. To the filtrate, was added diethyl ether, and the mixture was washed successively with a 3% sodium hydroxide aqueous solution, water and saturated saline solution, dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The resulting oily material was purified by silica gel column chromatography to obtain 29.7 g of the titled 5-methyl-1,4-benzodioxane (yield: 82%).
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