hydrogenchloride; methylmagnesium bromide in diethyl ether (N2); a soln. of B-compound cooled with a dry ice-acetone bath; a soln.of CH3MgBr added dropwise via syringe; stirred for 0.5 h; allowed to warm to room temp. with stirring for 0.5 h; cooled to 0°C; a soln. of HCl in ether added; warmed to room temp.; detected by (11)B NMR;