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首页> 外文期刊>Chemistry: A European journal >New chiral N-heterocyclic carbene ligands in palladium-catalyzed α-arylations of amides: Conformational locking through allylic strain as a device for stereocontrol
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New chiral N-heterocyclic carbene ligands in palladium-catalyzed α-arylations of amides: Conformational locking through allylic strain as a device for stereocontrol

机译：钯催化酰胺的α-芳基化反应中的新手性N-杂环卡宾配体：通过烯丙基应变构象锁定作为立体控制装置

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摘要

New 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 to 96 % ee) 3-alkyl-3-aryloxindole products were obtained in generally high yields (>95%) except in cases of steric congestion. The critical roles both of the bulky alkyl group and of the ortho-aryl substituent at the stereogenic center of the ligand were revealed in the crystal structure of a [Pd-(η~3-allyl)(NHC-L*)(I)] complex. The ligand aryl location and orientation is fixed by conformational locking that minimizes A~(1,3)-strain and enables optimal transfer of chiral information.
机译：已开发出新的Enders / Herrmann型手性N杂环卡宾（NHC）配体，并将其应用于不对称钯催化的酰胺内α-芳基化反应中。最好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在50°C下反应。除空间拥塞情况外，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-芳基吲哚产物。 [Pd-（η〜3-烯丙基）（NHC-L *）（I）的晶体结构揭示了大分子烷基和配体立体中心的邻芳基取代基的关键作用]复杂。配体芳基的位置和方向是通过构象锁定固定的，该构象锁定使A〜（1,3）应变降至最低，并实现了手性信息的最佳转移。

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