in tetrahydrofuran addn. of vinyl bromide and ethylene dibromide to Mg in THF (N2 atmosphere), addn. of further vinyl bromide in THF during 1 h at reflux, decantation, addn. of Sn-compd., refluxing (1 h), cooling room temp.); evapn., partition (Et2O-H2O), washing etheral phase (H2O), drying, evapn., distn.; elem. anal.;