iodine in tetrahydrofuran (N2), stirred for 30 min at room temp.; solvent removed, residue taken up in CH2Cl2, chromy.,;

bromine in tetrahydrofuran (N2), stirred for 30 min at room temp.; solvent removed, residue taken up in CH2Cl2, chromy.,;

iodine in tetrahydrofuran (N2), stirred for 30 min at room temp.; solvent removed, residue taken up in CH2Cl2, chromy.,;

 in  further solvent(s) stirring slowly, heating at a gentle flux, 25h; monitoring of the react. by IR; filtration, washing with CH2Cl2, drying in vac., recrystn. from CH2Cl2-hexanes at -40.egree.C; elem. anal.;