O2N PCL O2N NHPh H20 O2 COOH PhN Br oh B Br Ph NHCOPh O2N N PO 0 N一OH coOh Br Br Br The shift will keep the stereostructure of chiral center (2H5 CH2C2H5 H2SO4 CH2C2H5 H Et0 CH3CONH H HOBr N Ph O2N OH PCl5 H2O Br O O2N NHPh COOH Br O2N PhNH2 Br N Ph O2N OH PCl5 NHCOPh Br O2N H2O PhCOOH NH2 Br O2N Et 2O C CH3 C N HO C2H5 H CH2C2H5 H2 SO4 CH3CONH C C2H5 H CH2C2H5 The shift will keep the stereostructure of chiral center