CH CH H Br Br H BI H R Br H OH HO HH R OH HO H CH 2R,3R（2） CH3CHBr ― CHOH ― CH3 CH3 CH3 H Br H OH CH3 CH3 Br H HO H CH3 CH3 Br H H OH CH3 CH3 H Br HO H 2R,3R 2S,3S R S S R