Ethylene Glycol → 2-(3-Bromophenyl)-2-methyl-1,3-dioxolane

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Reaction Steps

5 g (25 mmol) of 3-bromoacetophenone are dissolved in 40 ml of toluene and then 15 ml of ethylene glycol and 500 mg of para-toluenesulphonic acid are added. The reaction medium is then heated under reflux equipped with a Dean-Stark distillation assembly. After 12 h, the medium is cooled and then treated with water and extracted with dichloromethane. After drying and concentrating, the residue is purified on a silica column in order to obtain the desired 3-(2-methyl-[1,3]dioxolan-2-yl)-1-bromobenzene (Y=85%). This product (4 g, 16.4 mmol) is then dissolved in anhydrous THF and the mixture is cooled to −78° C. 7.2 ml (18 mmol) of a 2.5M solution of butyllithium are then added dropwise. After stirring for 1 hour at the same temperature, 1.9 ml (18 mmol) of dimethylformamide are added. The mixture is maintained at −78° C. for 30 minutes and then brought to room temperature. The reaction medium is then treated with a saturated ammonium chloride solution and extracted with dichloromethane. After purification by chromatography on a silica column (ethyl acetate 10-heptane 90), a colourless oil is obtained (m=3.09 g; Y=98%).

Provenance & Evidence