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■ Synthesis of a Simple Kainic Acid Analogue by Means of Carbamoylmethyl Radical Cyclization

Tatsunori Sato, Ken-ichiro Matsubayashi, Kazumi Yamamoto, Hiroko Ishikawa, Hiroyuki Ishibashi, and Masazumi Ikeda

*Kyoto Pharmaceutical University, Misasagi, Yamashina, Kyoto 607-8414, Japan

Abstract

A new approach to (-)-(2S, 3R)-2-carboxy-3-pyrrolidineacetic acid (6) starting from D-serine is described. The key step is a radical cyclization of tert-butyl (S)-3-[2,2-dimethyl-N-[chloro(phenylthio)acetyl]oxazolidin-4-yl]-(E)-propenoate (15b), which gave tert-butyl (6S, 7R, 7aS)-5,6,7,7a-tetrahydro-3,3-dimethyl-5-oxo-6-phenylthio-1H,3H-pyrrolo[1,2-c]oxazol-7-ylacetate (16b) in a highly regio- and diastereo-selective manner. The compound (16b) was then converted into tert-butyl (4R, 5S)-5-(tert-butyldimethylsilyloxymethyl)-1-methoxycarbonyl-2-oxopyrrolidin-4-ylacetate (19) by standard chemical manipulations, which has already been transformed to 6.