共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
Enantioselective Synthesis of Tertiary Propargylic Alcohols under N‐Heterocyclic Carbene Catalysis 下载免费PDF全文
Eduardo Sánchez‐Díez Dr. Maitane Fernández Dr. Uxue Uria Prof. Efraim Reyes Prof. Luisa Carrillo Prof. Jose L. Vicario 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(23):8384-8388
A straightforward procedure to carry out the enantioselective benzoin reaction between aldehydes and ynones by employing a chiral N‐heterocyclic carbene (NHC) as catalyst was developed. Under the optimized reaction conditions, these ynones undergo a clean and selective 1,2‐addition with the catalytically generated Breslow intermediate, not observing any byproduct arising from competitive Stetter‐type reactivity. This procedure allows the preparation of tertiary alkynyl carbinols as highly enantioenriched materials, which have the remarkable potential to be used as chiral building blocks in organic synthesis. 相似文献
3.
Rachel M. Gillard Jared E. M. Fernando Prof. David W. Lupton 《Angewandte Chemie (International ed. in English)》2018,57(17):4712-4716
Herein we report the enantioselective N‐heterocyclic carbene catalyzed (4+2) annulation of the dienyl acyl azolium with enolates. The reaction exploits readily accessible acyl fluorides and TMS enol ethers to give a range of highly enantio‐ and diastereo‐enriched cyclohexenes (most >97:3 er and >20:1 dr). The reaction was found to require high nucleophilicity NHC catalysts with mechanistic studies supporting a stepwise 1,6‐addition/β‐lactonization. 相似文献
4.
Enantioselective N‐Heterocyclic Carbene Catalysis by the Umpolung of α,β‐Unsaturated Ketones 下载免费PDF全文
Yuji Nakano Prof. Dr. David W. Lupton 《Angewandte Chemie (International ed. in English)》2016,55(9):3135-3139
N‐Heterocyclic carbene‐catalyzed formation of β‐anionic intermediates from enones has been employed in the enantioselective synthesis of 2‐aryl propionates. The reaction was achievable using a homochiral 4‐MeOC6H4 morpholinone catalyst allowing the first example of enantioselective catalysis by umpolung of α,β‐unsaturated ketones. The reaction is high yielding, and shows robustness with reasonable generality. A mechanism is proposed in which the enantiodetermining protonation is achieved using either hexafluoroisopropanol or the formed naphthol product. 相似文献
5.
Dr. Alexey O. Chagarovskiy Dr. Vladimir S. Vasin Dr. Vladimir V. Kuznetsov Dr. Olga A. Ivanova Dr. Victor B. Rybakov Dr. Alexey N. Shumsky Prof. Dr. Nina N. Makhova Prof. Dr. Igor V. Trushkov 《Angewandte Chemie (International ed. in English)》2018,57(32):10338-10342
The first example of (3+3)‐annulation of two different three‐membered rings is reported herein. Donor‐acceptor cyclopropanes in reaction with diaziridines were found to afford perhydropyridazine derivatives in high yields and diastereoselectivity under mild Lewis acid catalysis. The disclosed reaction is applicable for the broad substrate scope and exhibits an excellent functional group tolerance. 相似文献
6.
Dr. Michael H. Wang Prof. Karl A. Scheidt 《Angewandte Chemie (International ed. in English)》2016,55(48):14912-14922
N‐Heterocyclic carbene (NHC) catalysis has emerged as a powerful stratagem in organic synthesis to construct complex molecules primarily by polarity reversal (umpolung) approaches. These unique Lewis bases have been used to generate acyl anions, enolates, and homoenolates in catalytic fashion. Recently, a new strategy has emerged that dramatically expands the synthetic utility of carbene catalysis by leveraging additional activation modes: cooperative catalysis. The careful selection and balance of cocatalysts have led to enhanced reactivity, increased yields, and improved stereoselectivity. In certain cases, these catalytic additives have changed the regioselectivity or diastereoselectivity. This Minireview highlights new advances in NHC cooperative catalysis and surveys the evolution of this field. 相似文献
7.
8.
Andreas Mavroskoufis Keerthana Rajes Paul Golz Arush Agrawal Vincent Ruß Jan P. Gtze Matthew N. Hopkinson 《Angewandte Chemie (International ed. in English)》2020,59(8):3190-3194
The combination of light activation and N‐heterocyclic carbene (NHC) organocatalysis has enabled the use of acid fluorides as substrates in a UVA‐light‐mediated photochemical transformation previously observed only with aromatic aldehydes and ketones. Stoichiometric studies and TD‐DFT calculations support a mechanism involving the photoactivation of an ortho‐toluoyl azolium intermediate, which exhibits “ketone‐like” photochemical reactivity under UVA irradiation. Using this photo‐NHC catalysis approach, a novel photoenolization/Diels–Alder (PEDA) process was developed that leads to diverse isochroman‐1‐one derivatives. 相似文献
9.
Enantioselective N‐Heterocyclic Carbene Catalyzed Cyclopentene Synthesis via the β‐Azolium Ylide 下载免费PDF全文
Lydia Scott Dr. Yuji Nakano Dr. Changhe Zhang Prof. David W. Lupton 《Angewandte Chemie (International ed. in English)》2018,57(32):10299-10303
Herein we report the cycloisomerization of electron‐poor 1,5‐dienes via the β‐azolium ylide to give enantioenriched cyclopentenes. The reaction is mediated by a chiral N‐heterocyclic carbene (NHC) catalyst, exploits readily available substrates, has good generality (17 examples), and displays excellent enantioselectivity (mostly >94:6). Studies demonstrating the viability of a related dynamic kinetic resolution are reported, as are those with alternate tethers and derivatizations. 相似文献
10.
Lewis Acid Catalyzed Enantioselective Desymmetrization of Donor–Acceptor meso‐Diaminocyclopropanes 下载免费PDF全文
Daniele Perrotta Ming‐Ming Wang Prof. Dr. Jérôme Waser 《Angewandte Chemie (International ed. in English)》2018,57(18):5120-5123
The first Lewis acid catalyzed enantioselective ring‐opening desymmetrization of a donor–acceptor meso‐diaminocyclopropane is reported. The copper(II)‐catalyzed Friedel–Crafts alkylation of indoles and one pyrrole with an unprecedented meso‐diaminocyclopropane delivered enantioenriched, diastereomerically pure urea products, which are structurally related to natural and synthetic bioactive compounds. The development of a new ligand through the investigation of an underexplored subclass of bis(oxazoline) ligands was essential for achieving high enantioselectivities. 相似文献
11.
Zhi‐Qin Liang Zhong‐Hua Gao Wen‐Qiang Jia Prof. Dr. Song Ye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(5):1868-1872
Bifunctional N‐heterocyclic carbenes with a free hydroxy group are demonstrated as efficient catalysts for the [3+4] annulation of enals with aurones to give the corresponding benzofuran‐fused ε‐lactones in good yields with good diastereoselectivities and excellent enantioselectivities. Control experiments reveal that the [3+4] cycloadducts are kinetically favored and could be transformed to the thermodynamically favored [3+2] cycloadducts with a non‐bifunctional NHC catalyst. 相似文献
12.
Yue Tang Idir Benaissa Mathieu Huynh Laure Vendier Noël Lugan Stphanie Bastin Philippe Belmont Vincent Csar Vronique Michelet 《Angewandte Chemie (International ed. in English)》2019,58(24):7977-7981
The synthesis and characterization of original NHC ligands based on an imidazo[1,5‐a]pyridin‐3‐ylidene (IPy) scaffold functionalized with a flanking barbituric heterocycle is described as well as their use as tunable ligands for efficient gold‐catalyzed C?N, C?O, and C?C bond formations. High activity, regio‐, chemo‐, and stereoselectivities are obtained for hydroelementation and domino processes, underlining the excellent performance (TONs and TOFs) of these IPy‐based ligands in gold catalysis. The gold‐catalyzed domino reactions of 1,6‐enynes give rise to functionalized heterocycles in excellent isolated yields under mild conditions. The efficiency of the NHC gold 5Me complex is remarkable and mostly arises from a combination of steric protection and stabilization of the cationic AuI active species by ligand 1Me . 相似文献
13.
14.
N‐Heterocyclic Carbene Catalysis via Azolium Dienolates: An Efficient Strategy for Remote Enantioselective Functionalizations 下载免费PDF全文
Dr. Xiang‐Yu Chen Qiang Liu Dr. Pankaj Chauhan Prof. Dr. Dieter Enders 《Angewandte Chemie (International ed. in English)》2018,57(15):3862-3873
N‐heterocyclic carbene (NHC) catalysis has emerged as a powerful strategy in organic synthesis. In recent years a number of reviews have been published on NHC‐catalyzed transformations involving Breslow intermediates, acyl azoliums, α,β‐unsaturated acyl azoliums, homoenolate equivalents, and azolium enolates. However, the azolium dienolate intermediates generated by NHCs have been employed in asymmetric synthesis only very recently, especially in cycloadditions dealing with remote functionalization. This Minireview highlights all the developments and the new advances in NHC‐catalyzed asymmetric cycloaddition reactions involving azolium dienolate intermediates. 相似文献
15.
N‐Heterocyclic Carbene Catalyzed Formal [3+2] Annulation Reaction of Enals: An Efficient Enantioselective Access to Spiro‐Heterocycles 下载免费PDF全文
Dr. Chang Guo Michael Schedler Constantin G. Daniliuc Prof. Dr. Frank Glorius 《Angewandte Chemie (International ed. in English)》2014,53(38):10232-10236
A highly enantioselective N‐heterocyclic carbene (NHC) catalyzed formal [3+2] annulation of α,β‐unsaturated aldehydes with azaaurones or aurone generating spiro‐heterocycles has been developed. The protocol represents a unique NHC‐activation‐based approach to access spiro‐heterocyclic derivatives bearing a quaternary stereogenic center with high optical purity (up to 95 % ee). 相似文献
16.
Dr. Changgui Zhao Fangyi Li Prof. Dr. Jian Wang 《Angewandte Chemie (International ed. in English)》2016,55(5):1820-1824
The dynamic kinetic resolution of 6‐hydroxypyranones with enals or alkynals through an asymmetric redox esterification is catalyzed by a chiral N‐heterocyclic carbene. The resulting esters are obtained in good to high yields and with high levels of enantio‐ and diastereocontrol. The reaction products are further derivatized to obtain functionalized sugar derivatives and natural products. 相似文献
17.
18.
An Iridium(I) N‐Heterocyclic Carbene Complex Catalyzes Asymmetric Intramolecular Allylic Amination Reactions 下载免费PDF全文
Dr. Ke‐Yin Ye Qiang Cheng Dr. Chun‐Xiang Zhuo Prof. Li‐Xin Dai Prof. Dr. Shu‐Li You 《Angewandte Chemie (International ed. in English)》2016,55(28):8113-8116
A chiral iridium(I) N‐heterocyclic carbene complex was reported for the first time as the catalyst in the highly enantioselective intramolecular allylic amination reaction. The current method provides facile access to biologically important enantioenriched indolopiperazinones and piperazinones in good yields (74–91 %) and excellent enantioselectivities (92–99 % ee). Preliminary mechanistic investigations reveal that the C?H activation occurs at the position ortho to the N‐aryl group of the ligand. 相似文献
19.
Dr. Suman De Sarkar Anup Biswas Ramesh C. Samanta Prof. Dr. Armido Studer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(15):4664-4678
This Concept article discusses the potential of oxidative carbene catalysis in synthesis and comprehensively covers pioneering studies as well as recent developments. Oxidative carbene catalysis can be conducted by using inorganic and organic oxidants. Applications in cascade processes, in enantioselective catalysis, and also in natural product synthesis are discussed. 相似文献
20.
Insights into the N‐Heterocyclic Carbene (NHC)‐Catalyzed Intramolecular Cyclization of Aldimines: General Mechanism and Role of Catalyst 下载免费PDF全文
Xue Li Dr. Mingsheng Tang Dr. Yanyan Wang Dr. Yang Wang Dr. Zhongjun Li Dr. Ling‐Bo Qu Dr. Donghui Wei 《化学:亚洲杂志》2018,13(13):1710-1718
One of the most challenging questions in the Lewis base organocatalyst field is how to predict the most electrophilic carbon for the complexation of N‐heterocyclic carbene (NHC) and reactant. This study provides a valuable case for this issue. Multiple mechanisms (A, B, C, D, and E) for the intramolecular cyclization of aldimine catalyzed by NHC were investigated by using density functional theory (DFT). The computed results reveal that the NHC energetically prefers attacking the iminyl carbon (AIC mode, which is associated with mechanisms A and C) rather than attacking the olefin carbon (AOC mode, which is associated with mechanisms B and D) or attacking the carbonyl carbon (ACC mode, which is associated with mechanism E) of aldimine. The calculated results based on the different reaction models indicate that mechanism A (AIC mode), which is associated with the formation of the aza‐Breslow intermediate, is the most favorable pathway. For mechanism A, there are five steps: (1) nucleophilic addition of NHC to the iminyl carbon of aldimine; (2) [1,2]‐proton transfer to form an aza‐Breslow intermediate; (3) intramolecular cyclization; (4) the other [1,2]‐proton transfer; and (5) regeneration of NHC. The analyses of reactivity indexes have been applied to explain the chemoselectivity, and the general principles regarding the possible mechanisms would be useful for the rational design of NHC‐catalyzed chemoselective reactions. 相似文献