先前对三唑基N-杂环卡宾的三唑离子共轭酸的三唑离子共轭酸的C(3)-氢/氘交换反应的研究表明,在酸性条件下,随着N1质子化成药用盐,其机理发生了变化。有趣的是,数据表明,相对于其他具有氢或甲基取代基而不是邻位氟的N-芳基取代基,在存在N-五氟苯基取代基的情况下,p K a N1的增加。探测氮的明显供体效应的存在五氟苯基取代基不同于该组中更常见的吸电子效果,我们研究了四种三唑鎓盐与N-芳基的2位和/或6位杂原子或杂原子取代基的类似氘交换反应戒指。这些包括具有N -2,4,6-三溴苯基11,N -2,6-二氯苯基12,N -2-吡啶基13和N -2-嘧啶基14取代基的三唑盐。日志ķ前- P d为型材11,12和14与先前研究的N-五氟苯基三唑鎓盐相比,发现在较低的p D s处显示出相似的趋势,因此支持了对p K a N1的明显供体效应。令人惊讶的是,N-吡啶盐13的log k ex -p D曲线在较低的p
Construction of Tropane Derivatives by the Organocatalytic Asymmetric Dearomatization of Isoquinolines
作者:Jin‐Hui Xu、Sheng‐Cai Zheng、Ji‐Wei Zhang、Xin‐Yuan Liu、Bin Tan
DOI:10.1002/anie.201605736
日期:2016.9.19
A chiral‐NHC‐catalyzed highly diastereo‐ and enantioselective dearomatizing double Mannich reaction of isoquinolines was developed that provides a powerful and straightforward synthetic route toward substituted tropane derivatives with four contiguous stereocenters. A unique feature of this strategy is the use of readily available isoquinolines to provide two reactive sites for dearomatization, thus
Oxidative Enantioselective α-Fluorination of Aliphatic Aldehydes Enabled by N-Heterocyclic Carbene Catalysis
作者:Fangyi Li、Zijun Wu、Jian Wang
DOI:10.1002/anie.201409473
日期:2014.10.27
Described is the first study on oxidativeenantioselective α‐fluorination of simple aliphatic aldehydes enabled by N‐heterocyclic carbene catalysis. N‐fluorobis(phenyl)sulfonimide serves as a an oxidant and as an “F” source. The CF bond formation occurs directly at the α position of simple aliphatic aldehydes, thus overcoming nontrivial challenges, such as competitive difluorination and nonfluorination
Enantioselective N-heterocyclic carbene-catalysed intermolecular crossed benzoin condensations: improved catalyst design and the role of <i>in situ</i> racemisation
作者:Eoghan G. Delany、Stephen J. Connon
DOI:10.1039/d0ob02017f
日期:——
N-aryl ring led to more chemoselective, efficient and enantioselective chemistry, however both quenching the reaction at different times and deuterium incorporation experiments involving the product revealed that this is complicated by product racemisation in situ (except in the case of benzoin itself), which explains the dependence of enantioselectivity on the electrophilicity of the reacting aldehydes
In this work, we provide a brief overview of the role of N-aryl substituents on triazolium N-heterocyclic carbene (NHC) catalysis. This synopsis provides context for the disclosed synthetic protocol for new chiral N-heterocyclic carbene (NHC) triazoliumsalts with brominated aromatic motifs. Incorporating brominated aryl rings into NHC structures is challenging, probably due to the substantial steric
Novel Chemoselective Reduction of Aryldiazonium Fluoroborates with Zn–NiCl2·6H2O–THF
作者:B. P. Bandgar、L. S. Uppalla
DOI:10.1039/a905588f
日期:——
Substituted aryldiazonium fluoroborates are selectively reduced to the corresponding phenylhydrazines by using ZnâNiCl2·6H2O in THF as a reducing agent.