in chloroform-d1 the Pb-compd. is stirred in dry CDCl3 at 60°C for 28 h; the reaction is monitored by 1H.-NMR, the solvent is evaporated off under reduced pressure, the residue is filtered in Et2O through silica gel, evapn. of solvent yielded a yellow oil, which is subjected to HPLC in AcOEt-light petroleum;