Metal-free catalytic enantioselective C-B bond formation: (pinacolato)boron conjugate additions to α,β-unsaturated ketones, esters, Weinreb amides, and aldehydes promoted by chiral N-heterocyclic carbenes.
Metal-free catalytic enantioselective C-B bond formation: (pinacolato)boron conjugate additions to α,β-unsaturated ketones, esters, Weinreb amides, and aldehydes promoted by chiral N-heterocyclic carbenes.
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无金属催化对映选择性的C-B键形成：（Pinacolato）硼缀合物添加到α，β-不饱和酮，酯，Weinreb酰胺和醛中，由手性N-杂球碳烯促进。
DOI：
10.1021/ja302929d
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发表时间：
2012-05-16
影响因子：
15
通讯作者：
Hoveyda, Amir H.
中科院分区：
文献类型：
--
作者：
Wu, Hao;Radomkit, Suttipol;O'Brien, Jeannette M.;Hoveyda, Amir H.
提出了第一个广泛适用于α，β-不饱和羰基的硼共轭加成（BCA）的无金属对映选择性方法。C-B键形成反应在2.5-7.5 mol %的易于获得的c1对称手性咪唑盐存在下进行，该盐被常见的有机碱1,8-重氮双环[5.4.0]十一-7-烯（dbu）原位转化为具有催化活性的非对映体和对映体纯n -杂环碳（NHC）。除了市售的双（pinacolato）二硼[B2(pin)2]外，与空间要求较低的非手性NHCs的反应相反，甲醇的存在是高效反应所必需的。无环和环α、β-不饱和酮类以及无环酯类、Weinreb酰胺类和醛类均可作为合适的底物；所需的β-硼基羰基分离率高达94%，对映体比（er）为bbb98:2。变换通常在环境温度下进行。在某些情况下，例如当使用反应性相对较低的不饱和酰胺时，需要升高温度（50-66℃）；尽管如此，反应仍然具有高度的对映选择性。通过与其他cu催化方法的比较，证明了nhc催化方法的实用性；在涉及多功能底物的情况下，通过无金属方法（例如，共轭加成与与炔、烯或醛的反应）显示出化学选择性的独特特征。
The first broadly applicable metal-free enantioselective method for boron conjugate addition (BCA) to α,β-unsaturated carbonyls is presented. The C–B bond forming reactions are promoted in the presence of 2.5–7.5 mol % of a readily accessible C1-symmetric chiral imidazolinium salt, which is converted, in situ, to the catalytically active diastereo- and enantiomerically pure N-heterocyclic carbene (NHC) by the common organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu). In addition to the commercially available bis(pinacolato)diboron [B2(pin)2], and in contrast to reactions with the less sterically demanding achiral NHCs, the presence of MeOH is required for high efficiency. Acyclic and cyclic α,β-unsaturated ketones, as well as acyclic esters, Weinreb amides and aldehydes can serve as suitable substrates; the desired β-boryl carbonyls are isolated in up to 94% yield and >98:2 enantiomer ratio (er). Transformations are often carried out at ambient temperature. In certain cases, such as when the relatively less reactive unsaturated amides are used, elevated temperatures are required (50–66 °C); nonetheless, reactions remain highly enantioselective. The utility of the NHC-catalyzed method is demonstrated through comparison with the alternative Cu-catalyzed protocols; in cases involving a polyfunctional substrate, unique profiles in chemoselectivity are exhibited by the metal-free approach (e.g., conjugate addition vs reaction with an alkyne, allene or aldehyde).
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影响因子：
16.6
作者：
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通讯作者：
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影响因子：
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通讯作者：
Hoveyda, Amir H.