in tetrahydrofuran byproducts: Bu2SnCl2; SbCl3 was added dropwise with stirring to soln. of Sn comp. (N2 or Ar);stirring for 2 h at 25°C; evapn., washing with pentane, Soxhlet extn. with pentane; elem. anal.;

1,5-diazabicyclo{4.3.0}non-5-ene in further solvent(s) in tetraglyme;