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1.
N. Chary Mamillapalli Prof. Govindasamy Sekar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(51):18584-18588
Synthesis of enantiomerically enriched α‐hydroxy amides and β‐amino alcohols has been accomplished by enantioselective reduction of α‐keto amides with hydrosilanes. A series of α‐keto amides were reduced in the presence of chiral CuII/(S)‐DTBM‐SEGPHOS catalyst to give the corresponding optically active α‐hydroxy amides with excellent enantioselectivities by using (EtO)3SiH as a reducing agent. Furthermore, a one‐pot complete reduction of both ketone and amide groups of α‐keto amides has been achieved using the same chiral copper catalyst followed by tetra‐n‐butylammonium fluoride (TBAF) catalyst in presence of (EtO)3SiH to afford the corresponding chiral β‐amino alcohol derivatives. 相似文献
2.
Dynamic Kinetic Asymmetric Transformations of β‐Stereogenic α‐Ketoesters by Direct Aldolization
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Michael T. Corbett Prof. Dr. Jeffrey S. Johnson 《Angewandte Chemie (International ed. in English)》2014,53(1):255-259
Dynamic kinetic asymmetric transformations (DyKAT) of racemic β‐bromo‐α‐keto esters by direct aldolization of nitromethane and acetone provide access to fully substituted α‐glycolic acid derivatives bearing a β‐stereocenter. The aldol adducts are obtained in excellent yield with high relative and absolute stereocontrol under mild reaction conditions. Mechanistic studies determined that the reactions proceed through a facile catalyst‐mediated racemization of the β‐bromo‐α‐keto esters under a DyKAT Type I manifold. 相似文献
3.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(26):7568-7572
An additive‐free nickel‐catalyzed α‐allylation of aldehydes with allyl alcohol is reported. The reaction is promoted by 1 mol % of in situ formed nickel complex in methanol, and water is the sole by‐product of the reaction. The experimental conditions allow the conversion of various α‐branched aldehydes and α,β‐unsaturated aldehydes as nucleophiles. The same catalyst and reaction conditions enabled a tandem aldol condensation of aldehyde/α‐allylation reaction. 相似文献
4.
gem‐Difluoroolefination of Diaryl Ketones and Enolizable Aldehydes with Difluoromethyl 2‐Pyridyl Sulfone: New Insights into the Julia–Kocienski Reaction
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Bing Gao Dr. Yanchuan Zhao Dr. Mingyou Hu Dr. Chuanfa Ni Prof. Dr. Jinbo Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7803-7810
The direct conversion of diaryl ketones and enolizable aliphatic aldehydes into gem‐difluoroalkenes has been a long‐standing challenge in organofluorine chemistry. Herein, we report efficient strategies to tackle this problem by using difluoromethyl 2‐pyridyl sulfone as a general gem‐difluoroolefination reagent. The gem‐difluoroolefination of diaryl ketones proceeds by acid‐promoted Smiles rearrangement of the carbinol intermediate; the gem‐difluoroolefination is otherwise difficult to achieve through a conventional Julia–Kocienski olefination protocol under basic conditions due to the retro‐aldol type decomposition of the key intermediate. Efficient gem‐difluoroolefination of aliphatic aldehydes was achieved by the use of an amide base generated in situ (from CsF and tris(trimethylsilyl)amine), which diminishes the undesired enolization of aliphatic aldehydes and provides a powerful synthetic method for chemoselective gem‐difluoroolefination of multi‐carbonyl compounds. Our results provide new insights into the mechanistic understanding of the classical Julia–Kocienski reaction. 相似文献
5.
Antonia Mielgo Dr. Irene Velilla Claudio Palomo Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(25):7496-7502
In the presence of p‐nitrobenzoic acid, the O‐nitroso aldol reaction of nitrosobenzene with enolisable aldehydes may be promoted by commercially available α,α‐diphenylprolinol trimethylsilyl ether. The reaction proceeds with good yields and essentially complete enantioselectivity, with catalyst loadings in the 5–10 mol % range. The resulting α‐oxyaldehyde adducts may be transformed in situ into α‐oxyimines, which provide 1,2‐amino alcohols upon treatment with Grignard reagents, in good overall yield (45–59 %) and with typical diastereomeric ratios ≥95:5. 相似文献
6.
Dr. Karin Weidner Zhongdong Sun Dr. Naoya Kumagai Prof. Dr. Masakatsu Shibasaki 《Angewandte Chemie (International ed. in English)》2015,54(21):6236-6240
A direct aldol reaction of an α‐azido 7‐azaindolinylamide, promoted by a Cu‐based cooperative catalyst, is documented. Aromatic aldehydes bearing an ortho substituent exhibited diastereodivergency depending on the nature of the chiral ligands used. Smooth reactions with ynals highlighted the broad substrate scope. A vicinal azido alcohol unit in the product allowed direct access to the corresponding aziridine and facile hydrolysis of the 7‐azaindolinylamide moiety furnished enantioenriched β‐hydroxy‐α‐azido carboxylic acid derivatives. 相似文献
7.
Zhaofeng Wang Xijian Li Prof. Dr. Yong Huang 《Angewandte Chemie (International ed. in English)》2013,52(52):14219-14223
Carbonyl‐substituted allenes are highly important synthetic intermediates for a number of heterocycles and strained‐ring systems. However, chemistry of allenyl aldehydes has not been explored as extensively as their ketone, ester, or amide analogues because of a lack of general synthetic methods. Described herein is the first direct α‐vinylidenation of aldehydes and an α‐vinylidenation/γ‐functionalization cascade to access tri‐ and tetrasubstituted allenyl aldehydes using a combination of a gold catalyst and an secondary amine. The reactive enamine intermediate of an aldehyde reacts with the gold‐activated hypervalent silylethynyl benziodoxolone to selectively generate the corresponding trisubstituted allenyl aldehyde. The allenyl aldehyde can further react with another equivalent of the alkynylation reagent or other electrophiles to afford tetrasubstituted allenes bearing an aldehyde group, an acetylene, and a halogen functionality. This method enables rapid access to polysubstituted furans from aldehydes. 相似文献
8.
An anti-selective direct catalytic asymmetric aldol reaction of thiolactam is described. A soft Lewis acid/hard Br?nsted base cooperative catalyst comprised of mesitylcopper/(R,R)-Ph-BPE exhibited high catalytic performance to produce an anti-aldol product with high stereoselectivity. The highly chemoselective nature of the present catalysis allows for the use of enolizable aldehydes as aldol acceptors. The diverse transformations of the thiolactam moiety highlight the synthetic utility of the present anti-aldol protocol. 相似文献
9.
Dr. Virginie Liautard Damien Jardel Clotilde Davies Muriel Berlande Dr. Thierry Buffeteau Dr. Dominique Cavagnat Dr. Frédéric Robert Dr. Jean‐Marc Vincent Prof. Dr. Yannick Landais 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14532-14539
Enantioselective aldol reactions between substituted pyridine carbaldehydes and α‐ketoacids were shown to provide isotetronic acids or their corresponding pyridinium salts, depending on the nature of the substituents on the pyridine ring. The pyridinium salts were generated through nucleophilic attack of the pyridine nitrogen atom onto the reactive keto functional group. Moderate‐to‐good yields of both compounds were typically obtained and high levels of enantioselectivity were observed by using benzimidazole pyrrolidine I as a catalyst. Hydrogenation of the resulting pyridinium salts led to new indolizidines with high ee values and diastereocontrol. X‐ray diffraction studies allowed the determination of the relative configuration of the products. Finally, DFT calculations were performed to rationalize the divergent pathway as a function of the pyridine substituents. 相似文献
10.
The one‐pot multicomponent coupling of an aromatic aldehyde, an enolizable ketone or keto ester, acetonitrile, and acetyl chloride at room temperature in the presence of Amberlyst‐15 as catalyst affords β‐acetamido ketones in high yields. The inexpensive catalyst works under heterogeneous conditions and can be readily reused. 相似文献
11.
Xiuqin Dong Wen Yang Weimin Hu Jianwei Sun 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(2):670-673
The asymmetric fluorination of azolium enolates that are generated from readily available simple aliphatic aldehydes or α‐chloro aldehydes and N‐heterocyclic carbenes (NHCs) is described. The process significantly expands the synthetic utility of NHC‐catalyzed fluorination and provides facile access to a wide range of α‐fluoro esters, amides, and thioesters with excellent enantioselectivity. Pyrazole was identified as an excellent acyl transfer reagent for catalytic amide formation. 相似文献
12.
N‐Heterocyclic Carbene Catalyzed Enantioselective α‐Fluorination of Aliphatic Aldehydes and α‐Chloro Aldehydes: Synthesis of α‐Fluoro Esters,Amides, and Thioesters
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Dr. Xiuqin Dong Dr. Wen Yang Dr. Weimin Hu Prof. Dr. Jianwei Sun 《Angewandte Chemie (International ed. in English)》2015,54(2):660-663
The asymmetric fluorination of azolium enolates that are generated from readily available simple aliphatic aldehydes or α‐chloro aldehydes and N‐heterocyclic carbenes (NHCs) is described. The process significantly expands the synthetic utility of NHC‐catalyzed fluorination and provides facile access to a wide range of α‐fluoro esters, amides, and thioesters with excellent enantioselectivity. Pyrazole was identified as an excellent acyl transfer reagent for catalytic amide formation. 相似文献
13.
Umpolung Reactions of α‐Imino Esters: Useful Methods for the Preparation of α‐Amino Acid Frameworks
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This paper summarizes our recent efforts toward the development of tandem reactions utilizing umpolung reactions of α‐imino esters. A highly diastereoselective tandem N‐alkylation–Mannich reaction of α‐imino esters was developed. A tandem N‐alkylation–addition reaction of α‐imino esters derived from ethyl glyoxylate with various aldehydes proceeded to give 1,2‐amino alcohols. The same reaction also proceeded efficiently using a novel flow system comprising two connected microreactors. Novel syntheses of α‐quaternary alkynyl amino esters and allenoates were developed through the use of umpolung N‐addition to β,γ‐alkynyl α‐imino esters, followed by regioselective acylation. In addition, a highly regioselective tandem N‐alkylation–vinylogous aldol reaction of β,γ‐alkenyl α‐imino esters was discovered. N‐Alkylation of α‐iminophosphonates followed by a Horner–Wadsworth–Emmons reaction with aldehydes occurred to afford enamines, which can be used in a four‐component coupling reaction with methyl vinyl ketone. α‐N‐Acyloxyimino esters served as highly efficient substrates for the N,N,C‐trialkylation reaction to introduce various nucleophiles at the imino nitrogen and carbon atoms. 相似文献
14.
Hexa‐ and nonanuclear titanium complexes were obtained by self‐assembly of titanium(IV)‐tert‐butoxide and D ‐mandelic acid. Suitable single crystals of these complexes were characterized by X‐ray structure analysis. When used with these complexes, aldol adducts were isolated with a high degree of regioselectivity in direct aldol additions of aromatic and aliphatic aldehydes to functionalized unsymmetrical ketones. High syn‐diastereoselectivities were obtained in aldol additions of enolizable aldehydes with hydroxyacetone and methoxyacetone. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
15.
Roman Pluta Naoya Kumagai Masakatsu Shibasaki 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2481-2485
α‐Oxygen‐functionalized amides found particular utility as enolate surrogates for direct aldol couplings with α‐fluorinated ketones in a catalytic manner. Because of the likely involvement of open transition states, both syn‐ and anti‐aldol adducts can be accessed with high enantioselectivity by judicious choice of the chiral ligands. A broad variety of alkoxy substituents on the amides and aryl and fluoroalkyl groups on the ketone were tolerated, and the corresponding substrates delivered a range of enantioenriched fluorinated 1,2‐dihydroxycarboxylic acid derivatives with divergent diastereoselectivity depending on the ligand used. The amide moiety of the aldol adduct was transformed into a variety of functional groups without protection of the tertiary alcohol, showcasing the synthetic utility of the present asymmetric aldol process. 相似文献
16.
Transition‐Metal‐Free α‐Arylation of Enolizable Aryl Ketones and Mechanistic Evidence for a Radical Process
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Martin Pichette Drapeau Indira Fabre Dr. Laurence Grimaud Dr. Ilaria Ciofini Prof. Dr. Thierry Ollevier Dr. Marc Taillefer 《Angewandte Chemie (International ed. in English)》2015,54(36):10587-10591
The α‐arylation of enolizable aryl ketones can be carried out with aryl halides under transition‐metal‐free conditions using KOtBu in DMF. The α‐aryl ketones thus obtained can be used for step‐ and cost‐economic syntheses of fused heterocycles and Tamoxifen. Mechanistic studies demonstrate the synergetic role of base and solvent for the initiation of the radical process. 相似文献
17.
A Facile Approach to Optically Active Hydroquinoline‐2‐carboxylates by a One‐Pot Asymmetric Michael/Transamination/Cyclization Process
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Dr. Chao Rong Hongjie Pan Dr. Mao Liu Hua Tian Dr. Yian Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):2887-2891
An efficient one‐pot synthesis of optically active hydroquinoline‐2‐carboxylates from 1,3‐cyclohexanediones, β,γ‐unsaturated α‐keto ester, and benzylamine in the presence of a chiral base catalyst and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) with good diastereoselectivity and high enantioselectivity is described. The reaction proceeds by a sequential asymmetric Michael/transamination/cyclization process. 相似文献
18.
Domino‐Hydroformylation/Aldol Condensation Catalysis: Highly Selective Synthesis of α,β‐Unsaturated Aldehydes from Olefins
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Xianjie Fang Dr. Ralf Jackstell Prof. Dr. Robert Franke Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13210-13216
A general and highly chemo‐, regio‐, and stereoselective synthesis of α,β‐unsaturated aldehydes by a domino hydroformylation/aldol condensation reaction has been developed. A variety of olefins and aromatic aldehydes were efficiently converted into various substituted α,β‐unsaturated aldehydes in good to excellent yields in the presence of a rhodium phosphine/acid–base catalyst system. In view of the easy availability of the substrates, the high atom‐efficiency, the excellent selectivity, and the mild conditions, this method is expected to complement current methodologies for the preparation of α,β‐unsaturated aldehydes. 相似文献
19.
Ludger A. Wessjohann Harry Wild Leonildo A. Ferreira Henri S. Schrekker 《应用有机金属化学》2016,30(8):674-679
The regioselective and diastereoselective chromium(II)‐mediated reactions of 4‐bromocrotonic acid or amides with aldehydes and ketones can proceed without the need to protect protic sites to generate the respective α‐alkenyl‐β‐hydroxy adducts, i.e. formally the addition of the α‐anion of a carboxylic acid or amide to an oxo‐compound is featured. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
20.
Xiaohong Chen Yin Zhu Zhen Qiao Mingsheng Xie Lili Lin Dr. Xiaohua Liu Dr. Xiaoming Feng Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(33):10124-10129
An easily available and efficient chiral N,N′‐dioxide–nickel(II) complex catalyst has been developed for the direct catalytic asymmetric aldol reaction of α‐isothiocyanato imide with aldehydes which produces the products in morderate to high yields (up to 98 %) with excellent diastereo‐ (up to >99:1 d.r.) and enantioselectivities (up to >99 % ee). A variety of aromatic, heteroaromatic, α,β‐unsaturated, and aliphatic aldehydes were found to be suitable substrates in the presence of 2.5 mol % L ‐proline‐derived N,N′‐dioxide L5 –nickel(II) complex. This process was air‐tolerant and easily manipulated with available reagents. Based on experimental investigations, a possible transition state has been proposed to explain the origin of reactivity and asymmetric inductivity. 相似文献