Kawabata Takeo, Kawakami Shimpei, Majumdar Swapan
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
J Am Chem Soc. 2003 Oct 29;125(43):13012-3. doi: 10.1021/ja0378299.
N-(omega-Bromoalkyl)-amino acid derivatives, readily prepared from natural alpha-amino acids, gave cyclic amino acids with a quaternary stereocenter by treatment with potassium hexamethyldisilazaide in DMF. The chirality of parent amino acids was almost completely preserved during an enolate-formation and cyclization process, giving aza-cyclic amino acids in up to 98% ee in retention of configuration. This method is applicable to the asymmetric synthesis of azetidine, pyrrolidine, piperidine, and azepane derivatives. The asymmetric cyclization seems to proceed via an axially chiral enolate intermediate and not through a concerted SEi process.
由天然α-氨基酸易于制备的N-（ω-溴代烷基）-氨基酸衍生物，在DMF中用六甲基二硅氮基钾处理后可得到具有季立体中心的环状氨基酸。在烯醇盐形成和环化过程中，母体氨基酸的手性几乎完全保留，得到构型保持的氮杂环氨基酸，对映体过量高达98%。该方法适用于氮杂环丁烷、吡咯烷、哌啶和氮杂环庚烷衍生物的不对称合成。不对称环化似乎是通过轴向手性烯醇盐中间体进行的，而不是通过协同的SEi过程。
