An efficient synthesis of (-)-chloramphenicol via asymmetric catalytic aziridination: A comparison of catalysts prepared from triphenylborate and various linear and vaulted biaryls

[GRAPHICS] The antibiotic (-)-choramphenicol has been synthesized in only four steps f rom p-nitro-benzaldehyde in optically pure form from an asymmetric catalyti c aziridination reaction with a chiral catalyst prepared from triphenylbora te and the (R)-VAPOL ligand. Catalysts generated from the VAPOL and VANOL l igands give much higher asymmetric induction than do catalysts prepared fro m 6,6'-diphenylVAPOL, BINOL, and BANOL ligands.