5-Methyl-4-bromothiophen-2-ylboronic acid

29421-73-6

154566-69-5

The general procedure for the synthesis of 4-bromo-5-methylthiophene-2-boronic acid from 3,5-dibromo-2-methylthiophene was as follows: 3,5-dibromo-2-methylthiophene (12.8 g, 50 mmol) was dissolved in anhydrous ether (240 mL) under argon protection and degassed. The solution was cooled to -78 °C and n-butyllithium (n-BuLi, 20.4 mL, 50 mmol, 2.5 M hexane solution) was added slowly and dropwise. The reaction mixture was stirred continuously at -78 °C for 30 min. Subsequently, tributyl borate (12.68 g, 50 mmol) was added and the reaction mixture was stirred overnight at room temperature. Upon completion of the reaction, 1 M HCl aqueous solution (200 mL) was added for acidification, and the ether phase was separated and extracted. The ether phase was washed three times with 1 M NaOH aqueous solution (3 x 70 mL). The NaOH phases were combined, concentrated and the pH was adjusted with HCl to 1. Under this acidic condition, the target product 4-bromo-5-methylthiophene-2-boronic acid precipitated as a beige solid in 76% yield.