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Paper | Special issue | Vol 47, No. 2, 1998, pp.765-780
Published online, 1st January, 1970
DOI: 10.3987/COM-97-S(N)71
■ Radical Reaction Initiated and Stereocontrolled by Zinc Chloride

Yoshinori Yamamoto,* Setsuko Onuki, Masatoshi Yumoto, and Naoki Asao

*Department of Chemistry, Graduate School of Science, Tohoku University, Aobayama, Sendai 980-8578, Japan

Abstract

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