New Chiral N-Heterocyclic Carbene Ligands in Palladium-Catalyzed α-Arylations of Amides: Conformational Locking through Allylic Strain as a Device for Stereocontrol
作者:Yi-Xia Jia、Dmitry Katayev、Gérald Bernardinelli、Thomas M. Seidel、E. Peter Kündig
DOI:10.1002/chem.201000031
日期:——
Enders/Herrmann‐type chiral N‐heterocyclic carbene (NHC) ligands have been developed and applied in asymmetric palladium‐catalyzed intramolecular α‐arylations of amides. The best ligands feature the bulky tert‐butyl group and ortho‐substituted aryl groups at the stereogenic centers. Aryl bromides readily react at room temperature and aryl chlorides at 50 °C. The highly enantiomerically enriched (up
已开发出新的Enders / Herrmann型手性N杂环卡宾(NHC)配体,并将其用于不对称钯催化的酰胺内α-芳基化反应。最佳的配体在立体异构中心具有庞大的叔丁基和邻位取代的芳基。芳基溴化物在室温下容易与芳基氯化物在50°C下反应。除空间拥塞外,通常以高收率(> 95%)获得高度对映体富集(最多ee为96% )的3-烷基-3-芳基吲哚产品。两个大的烷基和的关键作用的邻-芳基取代基的配位体的手性中心,揭示在[Pd所构成的晶体结构(η 3-allyl)(NHC-L *)(I)]复数。配体芳基的位置和方向通过构象锁定固定,该构象锁定可最大程度地减少1,3应变,并能最佳地传递手性信息。