in tetrahydrofuran under N2, dropwise addn. of boron-compd. in THF to a soln. of K(O-t-Bu) in THF at room temp., boiled under reflux for 30 min; solvent distd. off almost completely, dried under vac., treated with petroleum ether; elem. anal.;

NaNH2 in tetrahydrofuran under N2, dropwise addn. of boron-compd. in THF to a -78°C cold soln. of NaNH2 in THF, warmed to room temp.; all volatiles pumped off, treated with petroleum ether;