To a solution of 4,5-dibromo-2-thiophenecarboxylic acid (3.30 g, 11.54 mmol) in dioxane/H2O (4:1, 100 mL) was added K2CO3 (5.5 g, 40.0 mmol), tetrakistriphenylphosphine Pd(0) (671 mg, 0.58 mmol) and 5-(5,5-dimethyl-1,3,2-dioxaborinan-2-yl)-1-methyl-1H-pyrazole (2.66 g, 13.71 mmol). The reaction mixture was heated to 80° C. in a sealed tube for 12 hours. The reaction mixture was partitioned between H2O and CHCl3. The pH of the aqueous phase was adjusted to ˜3 with 6N HCl and washed several times with CHCl3. The combined organic fractions were dried (Na2SO4), concentrated under vacuum and used directly without further purification (3.3 g, quant.): LC-MS (ES) m/z=289 (M+H)+.
