Protonation-Assisted Conjugate Addition of Axially Chiral Enolates: Asymmetric Synthesis of Multisubstituted β-Lactams from α-Amino Acids
作者:Tomoyuki Yoshimura、Masatoshi Takuwa、Keisuke Tomohara、Makoto Uyama、Kazuhiro Hayashi、Pan Yang、Ryuichi Hyakutake、Takahiro Sasamori、Norihiro Tokitoh、Takeo Kawabata
DOI:10.1002/chem.201201339
日期:2012.11.26
prepared in a highly enantioselective manner through 4‐exo‐trig cyclization of axially chiral enolates generated from readily available α‐amino acids. Use of a weak base (metal carbonate) in a protic solvent (EtOH) is the key to the smooth production of β‐lactams. Use of the weak base is expected to generate the axially chiral enolates in a very low concentration, which undergo intramolecular conjugate addition
具有4个和3个取代碳原子中心的β-内酰胺是通过4 - exo -trig环化由容易获得的α-氨基酸产生的轴向手性烯醇化物以高度对映选择性的方式制备的。在质子传递溶剂(EtOH)中使用弱碱(金属碳酸盐)是顺利生产β-内酰胺的关键。预期使用弱碱会产生非常低浓度的轴向手性烯醇盐,其经历分子内共轭物加成而不会发生分子间副反应。因此通过可逆的分子内共轭物加成反应形成了高张力的β-内酰胺烯醇(4 -exo-trig轴向手性烯醇盐的环化反应)在反应介质中迅速被EtOH质子化(而不是在后处理过程中),以生成高达97%ee的β-内酰胺。