Oxalyl chloride → 2,3-Dichloro-4-methanesulfonylbenzoic acid 4-oxobicyclo[3.2.1]oct-2-en-2-yl ester

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Reaction Conditions

Reaction Steps

3.6 g of a 30% sodium methanolate solution (0.022 mol) are heated to a column head temperature of 108° C. in a mixture of 19 ml of toluene and 1 ml of dimethylformamide, methanol being removed by distillation. With removal of methanol by distillation being continued, 2.76 g (0.02 mol) of 4-methylene-3-oxabicyclo[3.2.1]octan-2-one dissolved in 3 ml of toluene are then added dropwise. After stirring for one hour, the mixture is cooled to a temperature of 20° C. and, while controlling the temperature, a solution in 1:1 toluene/acetonitrile of 6.32 g (0.022 mol) of 2,3-dichloro-4-methanesulfonylbenzoyl chloride freshly prepared with oxalyl chloride is introduced. After stirring briefly, extraction is carried out with a small amount of ethyl acetate against a slightly alkaline-aqueous solution at pH 10. 2,3-Dichloro-4-methanesulfonylbenzoic acid 4-oxobicyclo[3.2.1]oct-2-en-2-yl ester is obtained in the form of an amorphous crystallisate in a yield of 5.5 g (71%). 1H-NMR (DMSO-D6): 8.19 ppm, 2H, 5.85 ppm, s, 1H, 3.48 ppm, s, 3H, 3.07 ppm, m, 1H, 2.84 ppm, m, 1H, 1.9–2.2 ppm, 4H, 1.7 ppm, 2H.

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