lithium diisopropyl amide in tetrahydrofuran; hexane Li comp. in THF/hexane was added (Ar or N2) to soln. of Sn comp. in THF at -78°C, followed by addn. of t-BuBr; refluxing for 7 h; treatment with water, extn. of aq. layer with pentane, washing with water, drying (MgSO4), distn.; elem. anal.;