n-butyllithium in tetrahydrofuran dissolution of stannanes in THF and cooling to -78°C (CO2/acetone), dropwise addn. of BuLi in hexane via syringe, stirring at -78°C for 15 min, quenching by rapidly addn. of satd. aq. NH4Cl, warming to room temp.; diluting in petroleum ether, washing with sat. NaCL-solution, drying over Na2SO4, removing solvent under reduced pressure;