3-Chloro-2-methylphenylboronic acid, also known as (3-chloro-2-methyl)phenylboronic acid or 2-methyl-3-chlorophenylboronic acid, is a white solid powder. It is a widely used chemical intermediate, extensively used in the synthesis of pharmaceuticals and other fine chemical products.
(1) Acetal preparation: under the protection of nitrogen conditions, in a 1000mL three-necked flask, add 40g of 3-chloro-2-methylbenzaldehyde, 25g of ethylene glycol, 250ml of toluene, 4g of p-toluenesulphonic acid, heating and reflux splitting of water, after the end of the reaction, washed with a solution of potassium carbonate with a mass concentration of 30%, drying, desolvation and distillation of 3-chloro-2-methylbenzaldehyde ethylene glycol condensed pure 40g, the yield was 82%. The yield was 82%.
(2) lithiation: under the protection of nitrogen, in 1000mL dry three-necked flask, add 2-methyl-5-bromobenzaldehyde ethylene glycol prepared above, add 400ml tetrahydrofuran, lower the temperature to -80, and then add n-butyllithium 96ml dropwise, the dropwise process maintains the -80, the dropwise completion of the heat preservation reaction, control the reaction temperature of -80, to obtain the phenyl lithium compounds intermediates.
(3) Boronization: the obtained phenyl lithium compounds were cooled down to -80C, 60g of tributyl borate liquid was added dropwise to the solution of phenyl lithium prepared above, and after the dropwise addition was completed, the holding reaction was carried out, and the temperature of the holding reaction was -80C. The reaction was carried out at a controlled reaction temperature of -80C. After the end of the reaction, 10% hydrochloric acid of mass concentration was added to the reaction system and stirred, and the acetal was automatically deprotected during the stirring process, and the pH value of the reaction solution was adjusted to 1 to 2, and then the reaction solution was static stratified, extracted, and the organic layers were combined, dried, desolvated, and water was added to make up the water and then spun-dried and desolvated, and the generated butanol was spun off, and 26.4 g of 3-chloro-2-methylphenylboronic acid crude was obtained with a yield of 80%.
(4) Purification: add 26.4g 3-formyl-4-methylphenylboronic acid crude product in a 500ml conical flask, add ethyl acetate hot melt, then add 100ml petroleum ether, cooling, crystallization, centrifugation to get 23.07g 3-chloro-2-methylphenylboronic acid product, the yield is 70%.
