Alkylation of the hippurate esters of trans 2-(p-substituted phenyl)cyclohexanol with benzyl bromide affords phenylalanine derivatives in high chemical yield. The reaction stereoselectivity varies from 20 to >98% depending on the aromatic group in the cyclohexyl auxiliary. A model that correctly predicts the sense of the induction is proposed.
Selective Formation of Functionalized α-Quaternary Malononitriles toward 5,5-Disubstituted Pyrrolopyrimidinones
作者:Alan Whitehead、Yong Zhang、Jamie McCabe Dunn、Edward C. Sherer、Yu-hong Lam、John Stelmach、Aaron Sun、Melisa Shiroda、Robert K. Orr、Sherman T. Waddell、Subharekha Raghavan
DOI:10.1021/acs.orglett.7b01930
日期:2017.9.1
A modular, selective approach to complex α-tertiary substituted malononitriles is reported. The method takes advantage of β-ester-substituted α,α-dinitrile alkenes as highly reactive, chemoselective electrophiles for 1,4-additions with organometallic nucleophiles to produce functionally and sterically dense all-carbon quaternary centers. In the presence of a chiral ester auxiliary bearing an aromatic
[reaction: see text] New Lewis acid-assisted Bronsted acids (LBAs), tin(IV) chloride-2,6-dialkoxyphenols, serve as artificial cyclases for biomimeticpolyenecyclization. For example, the enantioselective cyclization of 4-(homogeranyl)toluene using tin(IV) chloride-2,6-di[(1'R,2'R)-trans-2'-(3' ',5' '-xylyl)cyclohexanoxy]phenol gave a trans-fused tricyclic compound with 85% ee.
Catalytic Hydrogen Atom Transfer (HAT) for Sustainable and Diastereoselective Radical Reduction
作者:Andreas Gansäuer、Max Klatte、Gerhard M. Brändle、Joachim Friedrich
DOI:10.1002/anie.201202818
日期:2012.8.27
Going cyclic! A catalytic cycle and cyclic transition states enable a novel sustainable and catalytichydrogenatomtransfer (HAT) for highly diastereoselectiveradicalreductions. Readily available nontoxic silanes are the terminal reductants for epoxides that are opened by bifunctional titanocene(III) hydride catalysts.
Asymmetric Induction via a Helically Chiral Anion: Enantioselective Pentacarboxycyclopentadiene Brønsted Acid-Catalyzed Inverse-Electron-Demand Diels–Alder Cycloaddition of Oxocarbenium Ions
作者:Chirag D. Gheewala、Jennifer S. Hirschi、Wai-Hang Lee、Daniel W. Paley、Mathew J. Vetticatt、Tristan H. Lambert
DOI:10.1021/jacs.8b00260
日期:2018.3.14
An enantioselective catalytic inverse-electron-demand Diels-Alder reaction of salicylaldehyde acetal-derived oxocarbenium ions and vinyl ethers to generate 2,4-dioxychromanes is described. Chiral pentacarboxycyclopentadiene (PCCP) acids are found to be effective for a variety of substrates. Computational and X-ray crystallographic analyses support the unique hypothesis that an anion with point-chirality-induced
描述了水杨醛缩醛衍生的氧代碳鎓离子和乙烯基醚的对映选择性催化逆电子需求 Diels-Alder 反应,以生成 2,4-二氧色满。发现手性五羧基环戊二烯 (PCCP) 酸对多种底物有效。计算和 X 射线晶体学分析支持独特的假设,即具有点手性诱导的螺旋手性的阴离子决定了该反应中立体化学的绝对意义。
Palladium-catalyzed asymmetric hydrogenation of 2-aryl cyclic ketones for the synthesis of <i>trans</i> cycloalkanols through dynamic kinetic resolution under acidic conditions
The first efficient palladium-catalyzed asymmetric hydrogenation of 2-aryl cyclic ketones has been described through dynamickineticresolution under acidic conditions, providing a facile access to chiral trans cycloalkanol derivatives with excellent enantioselectivities.