Asymmetric Base‐Free Michael Addition at Room Temperature with Nickel‐Based Bifunctional Amido‐Functionalized N‐Heterocyclic Carbene Catalysts
作者:Mitta Nageswar Rao、Meera Haridas、Manoj Kumar Gangwar、Palanisamy Rajakannu、Alok Ch. Kalita、Prasenjit Ghosh
DOI:10.1002/ejic.201403224
日期:2015.3
catalysts (1d–3d) with N-heterocyclic carbene (NHC) ligands derived from (1R)-(–)-menthol, (1S)-(–)pinene, and (1R)-(+)-camphor have been successfully designed for asymmetric Michael addition reactions under base-free conditions. The NHC complexes, namely, [1-R-3-N-(phenylacetamido)}imidazol-2-ylidene]2Ni [R = (1S)-menthyl (1d), (1S)-pinane (2d), and (1R)-isobornyl (3d)], bearing chiral ancillaries
一系列镍基手性双功能催化剂 (1d-3d) 具有衍生自 (1R)-(-)-薄荷醇、(1S)-(-)蒎烯和 (1R)-() 的 N-杂环卡宾 (NHC) 配体+)-樟脑已成功设计用于无碱条件下的不对称迈克尔加成反应。NHC 复合物,即 [1-R-3-N-(苯基乙酰胺基)}咪唑-2-亚基]2Ni [R = (1S)-薄荷基 (1d)、(1S)-蒎烷 (2d) 和 ( 1R)-异冰片基 (3d)],在 NHC 配体的酰胺基官能化侧臂上带有手性辅助物,对 α-甲基氰基酯底物 2-氰基丙酸乙酯的不对称无碱迈克尔加成反应进行双功能催化( 4), 2-氰基丙酸异丙酯 (5), 和 2-氰基丙酸叔丁酯 (6) 与活化的烯烃底物甲基乙烯基酮 (7) 和丙烯腈 (8) 的产率为 63–98%,室温下 8 小时对映体过量 (ee) 值为 2–75% . 更有趣的是,只有三种催化剂中最长的一种,薄荷醇衍生物 1d,显示出高达