An Amino Alcohol Ligand for Highly Enantioselective Addition of Organozinc Reagents to Aldehydes: Serendipity Rules
作者:William A. Nugent
DOI:10.1021/ol0259488
日期:2002.6.1
bis(2-bromoethyl) ether. Subsequent hydrogenation over 5% Rh on alumina in the presence of morpholine unexpectedly stops at the hexahydro derivative 4. Amino alcohol 4 promotes the enantioselectiveaddition of diethylzinc to aldehydes at room temperature in up to 99% enantiomeric excess.
Mechanism and scope of salen bifunctional catalysts in asymmetric aldehyde and α-ketoester alkylation
作者:Michael W. Fennie、Erin F. DiMauro、Erin M. O'Brien、Venkatachalam Annamalai、Marisa C. Kozlowski
DOI:10.1016/j.tet.2005.03.117
日期:2005.6
complexes of C2-symmetric Lewisacid/Lewis base salen ligands provide bifunctional activation resulting in rapid rates in the enantioselective addition of diethylzinc to aldehydes (up to 92% ee). Further experiments probed the reactivity of the individual Lewisacid and Lewis base components of the catalyst and established that both moieties are essential for asymmetriccatalysis. These catalysts are also
C 2对称的路易斯酸/路易斯碱塞伦配体的金属配合物提供双功能激活,从而使二乙基锌对醛的对映选择性加成速率加快(最高ee为92%)。进一步的实验探查了催化剂中各个路易斯酸和路易斯碱组分的反应性,并确定这两个部分对于不对称催化都是必不可少的。这些催化剂在将二乙基锌不对称加成到α-酮酸酯中也是有效的。这一发现意义重大,因为单独的α-酮酸酯充当其自身的配体,以加速Et 2的外消旋1,2-羰基加成反应锌与外消旋羰基还原。后者通过金属茂途径进行,并且通常占主要产物。奇异的路易斯酸催化剂不能在这两个竞争路径上加速对映选择性的1,2-加成。然而,双官能氨基塞伦催化剂以优异的收率,完全的化学选择性和良好的对映选择性(高达88%ee)快速提供对映体富集的1,2-加成产物。合成了双功能氨基塞隆的文库,并在该反应中进行了评估。已经在鸦片拮抗剂的合成中证明了α-酮酸酯方法的实用性。
Tail-Tied Ligands: An Immobilized Analogue of (R)-2-Piperidino-1,1,2-triphenylethanol with Intact High Catalytic Activity and Enantioselectivity
作者:Miquel A. Pericàs、David Castellnou、Israel Rodríguez、Antoni Riera、Lluís Solà
DOI:10.1002/adsc.200303125
日期:2003.12
A functional analogue of (R)-2-piperidino-1,1,2-triphenylethanol was synthesized and anchored to different polymeric supports by a position remote from the active region. This strategy, leading to what we call a tail-tiedligand, allows for the achievement of the optimal transition state geometry in the catalytic process. The catalyticactivity of the resulting heterogenized ligands was investigated
Salen-Derived Catalysts Containing Secondary Basic Groups in the Addition of Diethylzinc to Aldehydes
作者:Erin F. DiMauro、Marisa C. Kozlowski
DOI:10.1021/ol016535u
日期:2001.9.1
bifunctional salen catalysts which contain Lewis acid and Lewis base activating groups is described. These groups can be altered independently to control nucleophilic and electrophilic activation of the reacting substrates. These salen-derived catalysts show enhanced reactivity in the addition of diethylzinc to aldehydes with respect to most other salen, amino alcohol, and diamine derived catalysts and reactivity
Polystyrene-supported amino alcohol ligands for the heterogeneous asymmetric addition of phenyl zinc reagents to aldehydes
作者:David Castellnou、Montserrat Fontes、Ciril Jimeno、Daniel Font、Lluís Solà、Xavier Verdaguer、Miquel A. Pericàs
DOI:10.1016/j.tet.2005.07.112
日期:2005.12
A family of polystyrene-supported amino alcohols, characterized by a high catalytic activity in alkyl transfer from zinc to formyl groups has been successfully tested in the enantioselective addition of phenyl zinc reagents to aldehydes to afford chiral diarylmethanols. Enantioselectivities higher than 90% (mean ee 90.5%; eight examples) are recorded with aromatic aldehydes in what represents the first