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首页> 外文期刊>Chemistry: A European journal >Rh-catalyzed enantioselective conjugate addition of arylboronic acids with a dynamic library of chiral tropos phosphorus ligands
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Rh-catalyzed enantioselective conjugate addition of arylboronic acids with a dynamic library of chiral tropos phosphorus ligands

机译：Rh手性对位磷配体的动态文库对芳基硼酸的Rh催化对映选择性共轭加成

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摘要

A library of 19 chiral tropos phosphorus ligands, based on a free-to-rotate (tropos) biphenol unit and a chiral P-bonded alcohol (11 phosphites, 1-P(O)(2)O to 11-P(O)(2)O) or secondary amine (8 phosphoramidites, 12-P(O)(2)N to 19-P(O)(2)N), were screened, individually and in combinations of two, in the rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to enones and enoates. High enantioselectivities (up to 99 % ee) and excellent yields were obtained in the addition to either cyclic or acyclic substrates. The flexible biphenolic P ligands outperformed the analogous rigid binaphtholic P ligands. Variable-temperature P-31 NMR studies revealed that the biphenolic ligands are tropos even at low temperature. Only below 190 K was a coalescence observed; upon further cooling, two atropisomers were detected. The Rh homocomplexes ([Rh(L-a)2](+)) were also studied: in general, a single doublet (P-Rh coupling) was observed in the case of the biphenolic phosphite ligands, over the temperature range 380-230 K, demonstrating their tropos nature in the rhodium complexes even at low temperatures. On the other hand, the phosphoramidites showed different behaviors depending on the structure of the ligand and on the nature of the rhodium source. The spectrum at 230 K of the coalescence observed; upon further cooling, two atropisomers were detected. The Rh homocomplexes ([Rh(L-a)21(+)) were also studied: in general, a single doublet (P-Rh coupling) was observed in the case of the biphenolic phosphite ligands, over the temperature range 380-230 K, demonstrating their tropos nature in the rhodium complexes even at low temperatures. On the other hand, the phosphoramidites showed different behaviors depending on the structure of the ligand and on the nature of the rhodium source. The spectrum at 230 K of the mixture of [Rh(acac)(eth)(2)] (eth = C2H4) with phosphite 6-P(O)(2)O and lphosphoramidite 19-P(O)(2)N (the most enantioselective ligand combination in the conjugate addition reaction) revealed the presence of four homocomplexes (total approximately 40%: [Rh-{6-P(O)(2)O}(2)], [Rh{(aR)-19-P(O)(2)N-2], [Rh-(aR)-19-P(O)(2)N}(2)], [Rh{(aS)-19-P(O)(2)N-2}{(aS)-19-P(O)(2)N}]) and one heterocomplex, [Rh{6-P(O)(2)O}{(aR)-19-P(O)(2)N}] (approximately 60%) In the heterocomplex, the biphenol-derived phosphite is free to rotate (tropos) while the biphenol-derived phosphoramidite shows a temperature-dependent troposlatropos behavior (coalescence temperature= 310 K).
机译：基于自由旋转（对位）双酚单元和手性P键键合醇（11个亚磷酸酯，1-P（O）（2）O至11-P（O）的19个手性对位磷配体的库（2）O）或仲胺（8种亚磷酰胺，12-P（O）（2）N至19-P（O）（2）N），在铑催化下单独或两种组合筛选芳基硼酸向烯酮和烯酸酯的不对称共轭加成。除环状或非环状底物外，还具有较高的对映选择性（高达99％ee）和极好的收率。柔性双酚P配体的性能优于类似的刚性双萘酚P配体。可变温度P-31 NMR研究表明，即使在低温下，双酚配体也是对立的。仅在190 K以下观察到了聚结。进一步冷却后，检测到两种阻转异构体。还研究了Rh同络合物（[Rh（La）2]（+））：在双酚亚磷酸酯配体的情况下，通常在380-230 K的温度范围内观察到一个双峰（P-Rh偶联）。 ，即使在低温下也能证明它们在铑配合物中的对位性质。另一方面，亚磷酰胺显示出不同的行为，这取决于配体的结构和铑源的性质。观察到在230 K处的光谱合并;进一步冷却后，检测到两种阻转异构体。还研究了Rh同络合物（[Rh（La）21（+））：通常，在双酚亚磷酸酯配体的情况下，在380-230 K的温度范围内观察到单个双峰（P-Rh偶联），即使在低温下也能在铑配合物中证明其对位性质。另一方面，亚磷酰胺显示出不同的行为，这取决于配体的结构和铑源的性质。 [Rh（acac）（eth）（2）]（eth = C2H4）与亚磷酸酯6-P（O）（2）O和亚磷酰胺19-P（O）（2）N的混合物在230 K处的光谱（共轭加成反应中对映选择性最强的配体组合）显示存在四个均络合物（总计约40％：[Rh- {6-P（O）（2）O}（2）]，[Rh {（aR） -19-P（O）（2）N-2]，[Rh-（aR）-19-P（O）（2）N}（2）]，[Rh {（aS）-19-P（O ）（2）N-2} {（aS）-19-P（O）（2）N}]）和一个杂合物[Rh {6-P（O）（2）O} {（aR）-19 -P（O）（2）N}]（大约60％）在杂配合物中，双酚衍生的亚磷酸酯可自由旋转（对位），而双酚衍生的亚磷酰胺显示出与温度有关的对位错配行为（聚结温度= 310） K）。

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