Heterogeneous versus Homogeneous Copper(II) Catalysis in Enantioselective Conjugate-Addition Reactions of Boron in Water
Heterogeneous versus Homogeneous Copper(II) Catalysis in Enantioselective Conjugate-Addition Reactions of Boron in Water
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DOI：
10.1002/asia.201300997
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发表时间：
2014-01-01
影响因子：
4.1
通讯作者：
Kobayashi, Shu
中科院分区：
文献类型：
--
作者：
Kitanosono, Taku;Xu, Pengyu;Kobayashi, Shu
我们在水中开发了cu - ii催化的硼与-不饱和羰基化合物和-不饱和羰基化合物的对映选择性共轭加成反应。与之前报道的需要有机溶剂的Cu-I催化不同，手性Cu-II催化被发现在水中有效地进行。开发了三种催化剂体系：cat；1: Cu(OH)(2)与手性配体L1；猫。2: Cu(OH)(2)与乙酸配体L1；和猫。3: Cu(OAc)(2)配体L1。而猫。1是一个异构系统。2和猫。3个是齐次系统。我们测试了27种-不饱和羰基化合物和1种-不饱和腈化合物，包括无环和环，-不饱和酮，无环和环，-二取代烯酮，无环和环，-不饱和酯（包括它们的-二取代形式），以及无环，-不饱和酰胺（包括它们的-二取代形式）。我们找到了那只猫。2和猫。3对几乎所有底物均表现出较高的产率和对映选择性。值得注意的是，目前还没有报道过能耐受所有这些底物的高产率和高对映选择性的硼共轭加成催化剂。异构的猫。1对某些底物也有很高的产率和对映选择性，并且硼的不对称共轭加成反应的TOF最高（43200h(-1)）。此外，该催化剂体系也适用于将硼共轭加成到…-不饱和羰基化合物中，尽管这类反应在以前的文献中非常有限，甚至在有机溶剂中也是如此。用cat催化无环不饱和羰基化合物与二硼2反应，得到了产率高、对映选择性好的1,4加成产物。1、猫。2，或猫。另一方面，在环不饱和羰基化合物与化合物2的反应中，1,4加成产物只能通过cat反应得到。2或猫。3、1、6加成产物均由cat.1独家生产。在环三烯酮的反应中也表现出类似的独特反应活性和选择性。最后，研究了这些独特的共轭加成反应在水中的反应机理，并提出了由x射线晶体学和质谱（ESI）分析支持的立体化学模型。虽然水的作用尚未完全揭示，但预计水在激活硼铜（II）中间体和亲核加成步骤之后的质子化事件中是有效的，从而导致压倒性的高催化转化率。
We have developed Cu-II-catalyzed enantioselective conjugate-addition reactions of boron to ,-unsaturated carbonyl compounds and ,,,-unsaturated carbonyl compounds in water. In contrast to the previously reported Cu-I catalysis that required organic solvents, chiral Cu-II catalysis was found to proceed efficiently in water. Three catalyst systems have been exploited: cat.1: Cu(OH)(2) with chiral ligand L1; cat.2: Cu(OH)(2) and acetic acid with ligand L1; and cat.3: Cu(OAc)(2) with ligand L1. Whereas cat.1 is a heterogeneous system, cat.2 and cat.3 are homogeneous systems. We tested 27 ,-unsaturated carbonyl compounds and an ,-unsaturated nitrile compound, including acyclic and cyclic ,-unsaturated ketones, acyclic and cyclic ,-disubstituted enones, acyclic and cyclic ,-unsaturated esters (including their ,-disubstituted forms), and acyclic ,-unsaturated amides (including their ,-disubstituted forms). We found that cat.2 and cat.3 showed high yields and enantioselectivities for almost all substrates. Notably, no catalysts that can tolerate all of these substrates with high yields and high enantioselectivities have been reported for the conjugate addition of boron. Heterogeneous cat.1 also gave high yields and enantioselectivities with some substrates and also gave the highest TOF (43200h(-1)) for an asymmetric conjugate-addition reaction of boron. In addition, the catalyst systems were also applicable to the conjugate addition of boron to ,,,-unsaturated carbonyl compounds, although such reactions have previously been very limited in the literature, even in organic solvents. 1,4-Addition products were obtained in high yields and enantioselectivities in the reactions of acyclic ,,,-unsaturated carbonyl compounds with diboron 2 by using cat.1, cat.2, or cat.3. On the other hand, in the reactions of cyclic ,,,-unsaturated carbonyl compounds with compound 2, whereas 1,4-addition products were exclusively obtained by using cat.2 or cat.3, 1,6-addition products were exclusively produced by using cat.1. Similar unique reactivities and selectivities were also shown in the reactions of cyclic trienones. Finally, the reaction mechanisms of these unique conjugate-addition reactions in water were investigated and we propose stereochemical models that are supported by X-ray crystallography and MS (ESI) analysis. Although the role of water has not been completely revealed, water is expected to be effective in the activation of a borylcopper(II) intermediate and a protonation event subsequent to the nucleophilic addition step, thereby leading to overwhelmingly high catalytic turnover.