magnesium bromide in diethyl ether a soln. of MgBr2 in Et2O was added to magnesacyclobutane, mixt. was stirred for 30 min, Me2GeCl2 was added rapidly at room temp., stirring was continued for 1 h; water was added, ethereal layer was dried (MgSO4), ether was removed bycareful fractional distn.; >95percent purity according to (1)H NMR spectroscopy and GC anal.;