16694-17-0

3141-26-2

124-38-9

16694-17-0

Cool 100 mL of ether to -78°C under a nitrogen atmosphere. A 1.6 M n-butyllithium solution (28.4 mL) was slowly added. Subsequently, a solution of 3,4-dibromothiophene (10 g, 41.3 mmol) dissolved in 50 mL of ether was added dropwise over 10 min. The reaction temperature was maintained at -78 °C and stirring was continued for 10 min before an excess (>50 g) of fresh powdered dry ice (CO?) was added. The reaction mixture was stirred at -78°C for 1 hour, then 30 mL of 1 M NaOH solution (pre-diluted with 100 mL of water) was slowly added (note: CO? will be released). Gradually increase the temperature until the ice melts. Separate the organic and aqueous phases and extract the ether phase with 25 mL of 1 N NaOH solution. Combine all aqueous phases and acidify with 100 mL of 1 N HCl solution to pH < 7. Collect the precipitated white precipitate by filtration, wash with water, and dry in a vacuum oven to give 4-bromothiophene-3-carboxylic acid as a white solid (5.8 g, 68% yield).