To a solution of 4,5-dibromo-2-thiophenecarboxylic acid (1 g, 3.5 mmol) in dioxane/H2O (5:1, 18 mL) was added K2CO3 (1.9 g, 13.98 mmol), tetrakistriphenylphosphine Pd(0) (201 mg, 0.175 mmol) and 5-(5,5-dimethyl-1,3,2-dioxaborinan-2-yl)-1-methyl-1H-pyrazole (678 mg, 3.5 mmol). The reaction mixture was heated to 80° C. in a sealed tube for 12 h and was then partitioned between 6N NaOH and DCM. The pH of the aqueous phase was adjusted to ˜3 with 3M HCl and washed several times with DCM. The combined organic fractions were dried (Na2SO4), concentrated under vacuum and used directly without further purification (˜1 g, quant.): LC-MS (ES) m/z=288 (M+H)+.
