boron trifluoride diethyl etherate in dichloromethane under N2, a flask is charged with n-Bu3SnCH2OH, (MeO)2CH2, powdered 4-Å molecular sieves and CH2Cl2, boron trifluoride etherate is then added in one portion, suspn. is kept standing for 18 h; filtered, filtrate extd. with satd. NaHCO3 soln. and satd. NaCl soln., dried over Na2SO4, filtered, concd., distn.; elem. anal.;

in tetrahydrofuran Ar; butyltin-compound dissolved in THF cooled to -40 °C; LiBu added; stirred 15 min at -40 °C; Me3SnCl in THF was added; stirring 10 min;; poured into NH4Cl-soln. and petroleum ether; organic layer was separated, washed (brine); dried (Na2SO4); filtered; concd.; preparative TLC (ethyl acetate/petroleum ether 0.5:99.5);;