in dichloromethane dropwise addn. of Me4Sn to a soln. of the B-compound under Ar at room temp.;; evapn. of solvent and Me3SnCl, fractionated distn., elem. anal.;;

in dichloromethane under Ar, dropwise addn. of a soln. of Me3SC5Me5 to a soln. of the B-compound at -40°C, stirring (room temp., 1 h);; fractionated distn.;