RADICAL REACTION INITIATED AND STEREOCONTROLLED BY ZINC-CHLORIDE

The reaction of allyltributyltin with methyl -2-oxazolidinone-3-carbam oyl)amino]-2-bromoacetate (5a) was accelerated at -50 degrees C in the presence of AIBN and stopped in the presence of galvinoxyl, indicatin g that the reaction proceeds through a radical mechanism. The reaction was accelerated dramatically at -78 degrees C in the presence of ZnCl 2 . OEt2, and the ZnCl2-mediated reaction was stopped in the presence of galvinoxyl. In the presence of 2 equiv ZnCl2 . OEt2, the reaction a fforded methyl R)-2-[N-((4S)-4-(1-methylethyl)-2-oxazolidinone-3- carb amoyl)amino]4-pentenoate {6a(R)} with high diastereoselectivity (93:7) . Taken together, ZnCl2 . OEt2 works as a radical initiator as well as chelating agent.