9-Borabicyclo<3.3.1>nonan in tetrahydrofuran mixed THF soln. of cyclopropane derivative and 9-BBN at 0°C, stirring for 4 h, evapd. a part of solvent in dark and added HgAc2, stirred at room temp. for 5 h; mixed with n-pentane, washed with water, dried with MgSO4, then with CaH2, distd. in high vac., purity: 95percent (GC);