1: 2-bromothiophene-5-carboxylic acid tert-butyl ester With n-butyllithium in tetrahydrofuran T=-78°C; 0.5 h; 2: tri-isopropoxy-borane in tetrahydrofuran 2 h; 3: With water; ammonium chloride in tetrahydrofuran T=20°C;