boron trichloride; boron tribromide 1.) CH2Cl2, -50 deg C, 1 h then -20 deg C, 2h, 2.) CH2Cl2, room temp.; Yield given. Multistep reaction. Yields of byproduct given;

Multi-step reaction with 2 steps 1: BCl3 / CH2Cl2 2: 96 percent / K2CO3 / acetone / Heating