Ethyl bromoacetate → Ethyl 3-(6-Chloro-8-Methyl-2H-Chromen-3-yl)-2-Butenoate

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Reaction Steps

A volume of dimethoxymethane sufficient to cover 0.108 g-at. of zinc is added into a round-bottomed flask equipped with a stirrer, a dropping funnel, a condenser and a thermometer. A few drops of pure ethyl bromoacetate are then added. The reaction is primed by gentle heating (with the flame of a lighter). The reaction is then maintained by the dropwise addition of 0.1 mmol of ethyl bromoacetate dissolved in anhydrous dimethoxymethane. The rate of addition is adjusted so that the temperature does not exceed 40° C. After the addition, the reaction medium is stirred for a further 30 minutes at room temperature, and 0.083 mmol of 3-acetylchromene, dissolved in anhydrous THF, is then added in a single portion. The reaction medium is stirred for a further 15 minutes and then hydrolyzed with saturated ammonium chloride solution. After 3 successive extractions with ethyl acetate, the organic extracts are dried over magnesium sulfate and the solvents removed. 50 mmol of the expected product are dissolved in 50 ml of benzene and 1 ml of phosphorus oxychloride is added. The mixture is brought to reflux for 1 h 30 min. After being cooled, the reaction medium is poured into 100 ml of water. The benzene phase is decanted and the aqueous phase extracted with 2×50 ml of diethyl ether. After the organic extracts have been washed with saturated sodium hydrogen carbonate solution to neutrality and dried and the solvents have been removed, the ester is purified on a column of silica gel (SiO2 : 70-230 mesh; eluent CH2Cl2).

Provenance & Evidence