n-butyllithium; lithium diethylamide in tetrahydrofuran BuLi soln. (hexane) addn. to LiNEt2 soln. (THF) at 0°C, stirring 15 min, cooling to -78°C, stirring 1 h, Sn-compd. soln. (THF) addn., stirring 1.5 h, MeI addn., stirring 1.5 h, warming to room temp., vac. concn., diln. (Et2O); soln. washing (water, brine), org. phase drying (MgSO4), concn. (reducedpressure);