Nanocrystalline MgO for asymmetric Henry and Michael reactions
Nanocrystalline MgO for asymmetric Henry and Michael reactions
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DOI：
10.1021/ja0440248
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发表时间：
2005-09-28
影响因子：
15
通讯作者：
Sreedhar, B
中科院分区：
文献类型：
--
作者：
Choudary, BM;Ranganath, KVS;Sreedhar, B
具有三维结构和确定的尺寸和形状的纳米材料被认为是合适的候选者，用于与前手性基底进行适当的对准，用于单向引入反应物质以诱导不对称中心。本文首次报道了一种可回收的非均相催化剂纳米氧化镁的设计和开发，用于不对称亨利反应（AH），以优异的产率和良好至优异的对映选择性（ee's）提供手性硝基醇。布朗斯台德羟基是ee的唯一贡献者，而它们增加了AH的活性。结果表明，（S）-（-）-联苯二酚的-OH基团与MgO的-OH基团之间的氢键相互作用是诱导对映体选择性的必要条件。此外，为了证明上述假设，我们已经成功地进行了另一个反应，不对称迈克尔反应（AM）与纳米MgO。可重复使用的和适当排列的纳米晶MgO催化的AH和AM反应提供了手性产物，具有可比的ee的均匀系统。
Nanomaterials with their three-dimensional structure and defined size and shape are considered to be suitable candidates for proper alignment with prochiral substrates for unidirectional introduction of reacting species to induce an asymmetric center. We herein report the design and development of a truly recyclable heterogeneous catalyst, nanocrystalline magnesium oxide, for the asymmetric Henry reaction (AH) to afford chiral nitro alcohols with excellent yields and good to excellent enantioselectivities (ee's) for the first time. Bronsted hydroxyls are the sole contributors for the ee, while they add on to the activity in AH. It is demonstrated that the hydrogen bond interactions between the -OH groups of (S)-(-)-binol and the -OH groups of MgO are essential for the induction of enantioselectivity. Further, to prove the above hypothesis, we have successfully carried out another reaction, asymmetric Michael reaction (AM) with nanocrystalline MgO. The reusable and suitably aligned nanocrystalline MgO-catalyzed AH and AM reactions afforded chiral products with comparable ee's to that of the homogeneous system.