in diethyl ether dropwise addn. of soln. of Mg-compd. in diethyl ether to etheric soln. of Hg-compd. with stirring at -30°C, warming to -5°C, further stirring for 1.5 h; addn. of H2O (with ice cooling), sepn. of ether phase, drying over MgSO4, distillation, elem. anal.;