in diethyl ether N2-atmosphere; addn. of mesityl bromide (in Et2O) to Mg, filtration, cooling to -20°C, addn. of SnCl4 (in light petroleum), stirring (room temp., 15 h), refluxing (2 h); filtration, concentrating, trituration with light petroleum, recrystn. (light petroleum); total yield 30percent; mixt. of products (Cl2:BrCl:Br2 derivative=3:30:67) not sepd., detd. by (119)Sn-NMR spectroscopy;