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1.
Synthesis of Branched‐Chain Sugars with a DHAP‐Dependent Aldolase: Ketones are Electrophile Substrates of Rhamnulose‐1‐phosphate Aldolases
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Victor Laurent Dr. Ekaterina Darii Angelina Aujon Marine Debacker Jean‐Louis Petit Dr. Virgil Hélaine Dr. Tibor Liptaj Martin Breza Aline Mariage Lionel Nauton Dr. Mounir Traïkia Dr. Marcel Salanoubat Prof. Dr. Marielle Lemaire Dr. Christine Guérard‐Hélaine Dr. Véronique de Berardinis 《Angewandte Chemie (International ed. in English)》2018,57(19):5467-5471
Dihydroxyacetone phosphate (DHAP)‐dependent rhamnulose aldolases display an unprecedented versatility for ketones as electrophile substrates. We selected and characterized a rhamnulose aldolase from Bacteroides thetaiotaomicron (RhuABthet) to provide a proof of concept. DHAP was added as a nucleophile to several α‐hydroxylated ketones used as electrophiles. This aldol addition was stereoselective and produced branched‐chain monosaccharide adducts with a tertiary alcohol moiety. Several aldols were readily obtained in good to excellent yields (from 76 to 95 %). These results contradict the general view that aldehydes are the only electrophile substrates for DHAP‐dependent aldolases and provide a new C?C bond‐forming enzyme for stereoselective synthesis of tertiary alcohols. 相似文献
2.
Fe(OTf)3‐Catalyzed α‐Benzylation of Aryl Methyl Ketones with Electrophilic Secondary and Aryl Alcohols
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Acid‐catalyzed Friedel–Crafts alkylation of 1,3‐dicarbonyl compounds with electrophilic alcohols, is known to be an effective C? C bond forming reaction. However, until now, this reaction has not been amenable for α‐alkylation of aryl methyl ketones because of the notoriously low nucleophilicities of these compounds. Therefore, α‐alkylation of aryl methyl ketone relies on precious metal catalysts and also, the use of primary alcohols is mandatory. In this study, we found that a system composed of a Fe(OTf)3 catalyst and chlorobenzene solvent is sufficient to promote the title Friedel–Crafts reaction by using benzhydrols as electrophiles. 3,4‐Dihydro‐9‐(2‐hydroxy‐4,4‐dimethyl‐6‐oxo‐1‐cyclohexen‐1‐yl)‐3,3‐dimethyl‐xanthen‐1(2 H)‐one was also applicable as an electrophile in this type of benzylation reaction. On the basis of this result, a three‐component reaction of salicylaldehyde, dimedone, and aryl methyl ketone was also developed, and this provided an efficient way for the synthesis of densely substituted 4H‐chromene derivatives. 相似文献
3.
Gabriele Pupo Dr. Roberta Properzi Prof. Dr. Benjamin List 《Angewandte Chemie (International ed. in English)》2016,55(20):6099-6102
Quaternary stereocenters are found in numerous bioactive molecules. The Tsuji–Trost reaction has proven to be a powerful C?C bond forming process, and, at least in principle, should be well suited to access quaternary stereocenters via the α‐allylation of ketones. However, while indirect approaches are known, the direct, catalytic asymmetric α‐allylation of branched ketones has been elusive until today. By combining “enol catalysis” with the use of CO2 as a formal catalyst for asymmetric catalysis, we have now developed a solution to this problem: we report a direct, highly enantioselective and highly atom‐economic Tsuji–Trost allylation of branched ketones with allylic alcohol. Our reaction delivers products bearing quaternary stereocenters with high enantioselectivity and water as the sole by‐product. We expect our methodology to be of utility in asymmetric catalysis and inspire the design of other highly atom‐economic transformations. 相似文献
4.
Prof. Sanzhong Luo Prof. Jin‐Pei Cheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(46):15669-15681
Enantioselective protonation with a catalytic enamine intermediate represents a challenging, yet fundamentally important process for the synthesis of α‐chiral carbonyls. We describe herein chiral primary‐amine‐catalyzed conjugate additions of indoles to both α‐substituted acroleins and vinyl ketones. These reactions feature enamine protonation as the stereogenic step. A simple primary–tertiary vicinal diamine 1 with trifluoromethanesulfonic acid (TfOH) was found to enable both of the reactions of acroleins and vinyl ketones with good activity and high enantioselectivity. Detailed mechanistic studies reveal that these reactions are rate‐limiting in iminium formation and they all involve a uniform H2O/acid‐bridged proton transfer in the stereogenic steps but divergent stereocontrol modes for the protonation stereoselectivity. For the reactions of α‐branched acroleins, facial selections on H2O‐bridged protonation determine the enantioselectivity, which is enhanced by an OH???π interaction with indole as uncovered by DFT calculations. On the other hand, the stereoselectivity of the reactions with vinyl ketones is controlled according to the Curtin–Hammett principle in the C? C bond‐formation step, which precedes a highly stereospecific enamine protonation. 相似文献
5.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(2):524-536
Ynolates were found to react with α‐alkoxy‐, α‐siloxy‐, and α‐aryloxyketones at room temperature to afford tetrasubstituted olefins with high Z selectivity. Since the geometrical selectivity was determined in the ring opening of the β‐lactone enolate intermediates, the torquoselectivity was controlled by the ethereal oxygen atoms. From experimental and theoretical studies, the high Z selectivity is induced by orbital and steric interactions rather than by chelation. In a similar manner, α‐dialkylamino ketones provided olefins with excellent Z selectivity. These products can be easily converted into multisubstituted butenolides and γ‐butyrolactams in good yield. 相似文献
6.
Palladium(II)‐Catalyzed ortho‐CH Arylation/Alkylation of N‐Benzoyl α‐Amino Ester Derivatives
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Dr. Luis C. Misal Castro Prof. Naoto Chatani 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4548-4553
The palladium‐catalyzed arylation/alkylation of ortho‐C?H bonds in N‐benzoyl α‐amino ester derivatives is described. In such a system both the NH‐amido and the CO2R groups in the α‐amino ester moieties play a role in successful C?H activation/C?C bond formation using iodoaryl coupling partners. A wide variety of functional groups and electron‐rich/deficient iodoarenes are tolerated. The yields obtained range from 20 to 95 %. 相似文献
7.
An N‐heterocyclic carbene/nickel‐catalyzed direct coupling of alcohols and internal alkynes to form α‐branched ketones has been developed. This methodology provides a new approach to afford branched ketones, which are difficult to access through the hydroacylation of simple internal alkenes with aldehydes. This redox‐neutral and redox‐economical coupling is free from any oxidative or reductive additives as well as stoichiometric byproducts. These reactions convert both benzylic and aliphatic alcohols and alkynes, two basic feedstock chemicals, into various α‐branched ketones in a single chemical step. 相似文献
8.
Catalyst‐Free Dehydrative α‐Alkylation of Ketones with Alcohols: Green and Selective Autocatalyzed Synthesis of Alcohols and Ketones
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Prof. Dr. Qing Xu Jianhui Chen Haiwen Tian Xueqin Yuan Shuangyan Li Chongkuan Zhou Dr. Jianping Liu 《Angewandte Chemie (International ed. in English)》2014,53(1):225-229
Direct dehydrative α‐alkylation reactions of ketones with alcohols are now realized under simple, practical, and green conditions without using external catalysts. These catalyst‐free autocatalyzed alkylation methods can efficiently afford useful alkylated ketone or alcohol products in a one‐pot manner and on a large scale by C?C bond formation of the in situ generated intermediates with subsequent controllable and selective Meerwein–Pondorf–Verley–Oppenauer‐type redox processes. 相似文献
9.
Ru‐Catalyzed Branched versus Linear Selective C3‐Alkylation of 2‐Aroylbenzofurans with Acrylates via CH Activation
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Yadagiri Kommagalla Kolluru Srinivas Dr. Chepuri V. Ramana 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):7884-7889
The carbonyl‐directed C3?H activation and alkylation of 2‐aroylbenzo[b]furans with acrylates occurs selectively either in a linear or branched fashion, depending on the catalyst employed; [Ru(p‐cymene)Cl2]2 or Ru(PPh3)3Cl2, respectively. Two alternate pathways—funded upon the differences in steric and electronic preferences of these two complexes—is proposed for the selectivity of linear versus branched products. 相似文献
10.
C‐Alkylation of Ketones and Related Compounds by Alcohols: Transition‐Metal‐Catalyzed Dehydrogenation
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Fei Huang Zhuqing Liu Prof. Dr. Zhengkun Yu 《Angewandte Chemie (International ed. in English)》2016,55(3):862-875
Transition‐metal‐catalyzed C‐alkylation of ketones and secondary alcohols, with alcohols, avoids use of organometallic or environmentally unfriendly alkylating agents by means of borrowing hydrogen (BH) or hydrogen autotransfer (HA) activation of the alcohol substrates. Water is formed as the only by‐product, thus making the BH process atom‐economical and environmentally benign. Diverse homogeneous and heterogeneous transition‐metal catalysts, ketones, and alcohols can be used for this transformation, thus rendering the BH process promising for replacing those procedures that use traditional alkylating agents. This Minireview summarizes the advances during the last five years in transition‐metal‐catalyzed BH α‐alkylation of ketones, and β‐alkylation of secondary alcohols with alcohols. A discussion on the application of the BH strategy for C?C bond formation is included. 相似文献
11.
《Journal of heterocyclic chemistry》2017,54(1):137-146
The transformation of 1,2,3‐thiadiazolyl hydrazones of aldehydes and ketones including Dimroth rearrangement giving 1‐alkylidenamino‐5‐mercapto‐1,2,3‐triazoles, alkylation of mercapto group of these heterocyclic compounds by α‐bromoacetophenones and cyclization giving 6,7‐dihydro‐5H‐[1,2,3]triazolo[5,1‐b ][1,3,4]thiadizines have been investigated. It was shown that the reaction for hydrazones of acetophenones and benzoaldehydes is diastereoselective. Triazolothiadiazine spiro derivatives were prepared with transformation of hydrazones of cyclic ketones. 相似文献
12.
Wen Ai Xueyan Yang Yunxiang Wu Xuan Wang Prof. Yuanchao Li Dr. Yaxi Yang Dr. Bing Zhou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(52):17653-17657
A RhIII‐catalyzed procedure for the C7‐selective C?H alkylation of various indolines with α‐diazo compounds at room temperature is reported. The advantages of this process are: 1) simple, mild, and pH‐neutral reaction conditions, 2) broad substrate scope, 3) complete regioselectivity, 4) no need for an external oxidant, and 5) N2 as the sole byproduct. Furthermore, alkylation and bis‐alkylation of carbazoles at the C1 and C8 positions have also been developed. More significantly, for the first time, a successful IrIII‐catalyzed intermolecular insertion of arene C?H bonds into α‐diazo compounds is reported. 相似文献
13.
Gonzalo Blay Dr. Isabel Fernández Dr. M. Carmen Muñoz Prof. Dr. José R. Pedro Prof. Dr. Carlos Vila 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(30):9117-9122
Chiral complexes of BINOL‐based ligands with zirconium tert‐butoxide catalyze the Friedel–Crafts alkylation reaction of indoles with β‐trifluoromethyl‐α,β‐unsaturated ketones to give functionalized indoles with an asymmetric tertiary carbon center attached to a trifluoromethyl group. The reaction can be applied to a large number of substituted α‐trifluoromethyl enones and substituted indoles. The expected products were obtained with good yields and ees of up to 99 %. 相似文献
14.
Asymmetric anti‐Selective Michael Reaction of Imidazole‐Modified Ketones with trans‐β‐Nitroalkenes
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Dongxu Yang Linqing Wang Dan Li Fengxia Han Dr. Depeng Zhao Prof. Dr. Rui Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1458-1462
The successful application of imidazole‐modified ketones in asymmetric anti‐selective Michael reactions with trans‐β‐nitroalkenes is presented by employing a newly developed 3‐bromothiophene‐modified chiral diamine ligand. The corresponding conjugate adduct was submitted to further transformations with Grignard reagents to solve the problem of α‐site selectivity of simple linear ketones. Additionally, the syn‐selective product was obtained by treating the anti‐selective adduct with a simple base. In this way, the site‐specific products for both diastereomers in the asymmetric conjugate addition of simple ketones to nitroalkenes can be obtained. 相似文献
15.
Design of New Ligands for the Palladium‐Catalyzed Arylation of α‐Branched Secondary Amines
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Nathaniel H. Park Ekaterina V. Vinogradova Dr. David S. Surry Prof. Dr. Stephen L. Buchwald 《Angewandte Chemie (International ed. in English)》2015,54(28):8259-8262
In Pd‐catalyzed C? N cross‐coupling reactions, α‐branched secondary amines are difficult coupling partners and the desired products are often produced in low yields. In order to provide a robust method for accessing N‐aryl α‐branched tertiary amines, new catalysts have been designed to suppress undesired side reactions often encountered when these amine nucleophiles are used. These advances enabled the arylation of a wide array of sterically encumbered amines, highlighting the importance of rational ligand design in facilitating challenging Pd‐catalyzed cross‐coupling reactions. 相似文献
16.
A 3,4‐trans‐Fused Cyclic Protecting Group Facilitates α‐Selective Catalytic Synthesis of 2‐Deoxyglycosides
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Dr. Edward I. Balmond Dr. David Benito‐Alifonso Dr. Diane M. Coe Prof. Roger W. Alder Dr. Eoghan M. McGarrigle Dr. M. Carmen Galan 《Angewandte Chemie (International ed. in English)》2014,53(31):8190-8194
A practical approach has been developed to convert glucals and rhamnals into disaccharides or glycoconjugates with high α‐selectivity and yields (77–97 %) using a trans‐fused cyclic 3,4‐O‐disiloxane protecting group and TsOH?H2O (1 mol %) as a catalyst. Control of the anomeric selectivity arises from conformational locking of the intermediate oxacarbenium cation. Glucals outperform rhamnals because the C6 side‐chain conformation augments the selectivity. 相似文献
17.
α‐Aminoxy‐Acid‐Auxiliary‐Enabled Intermolecular Radical γ‐C(sp3)−H Functionalization of Ketones
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Dr. Heng Jiang Prof. Dr. Armido Studer 《Angewandte Chemie (International ed. in English)》2018,57(6):1692-1696
A method for site‐specific intermolecular γ‐C(sp3)?H functionalization of ketones has been developed using an α‐aminoxy acid auxiliary applying photoredox catalysis. Regioselective activation of an inert C?H bond is achieved by 1,5‐hydrogen atom abstraction by an oxidatively generated iminyl radical. Tertiary and secondary C‐radicals thus formed at the γ‐position of the imine functionality undergo radical conjugate addition to various Michael acceptors to provide, after reduction and imine hydrolysis, the corresponding γ‐functionalized ketones. 相似文献
18.
Practical Synthesis of anti‐β‐Hydroxy‐α‐Amino Acids by PdII‐Catalyzed Sequential C(sp3)H Functionalization
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Kai Chen Shuo‐Qing Zhang Huai‐Zhi Jiang Jing‐Wen Xu Prof. Dr. Bing‐Feng Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3264-3270
An improved and practical procedure for the stereoselective synthesis of anti‐β‐hydroxy‐α‐amino acids (anti‐βhAAs), by palladium‐catalyzed sequential C(sp3)?H functionalization directed by 8‐aminoquinoline auxiliary, is described. followed by a previously established monoarylation and/or alkylation of the β‐methyl C(sp3)?H of alanine derivative, β‐acetoxylation of both alkylic and benzylic methylene C(sp3)?H bonds affords various anti‐β‐hydroxy‐α‐amino acid derivatives. As an example, the synthesis of β‐mercapto‐α‐amino acids, which are highly important to the extension of native chemical ligation chemistry beyond cysteine, is described. The synthetic potential of this protocol is further demonstrated by the synthesis of diverse β‐branched α‐amino acids. The observed diastereoselectivities are strongly influenced by electronic effects of aromatic AAs and steric effects of the linear side‐chain AAs, which could be explained by the competition of intramolecular C?OAc bond reductive elimination from PdIV intermediates vs. intermolecular attack by an external nucleophile (AcO?) in an SN2‐type process. 相似文献
19.
Saravanakumar Elangovan Dr. Jean‐Baptiste Sortais Prof. Dr. Matthias Beller Prof. Dr. Christophe Darcel 《Angewandte Chemie (International ed. in English)》2015,54(48):14483-14486
A general and benign iron‐catalyzed α‐alkylation reaction of ketones with primary alcohols has been developed. The key to success of the reaction is the use of a Knölker‐type complex as catalyst (2 mol %) in the presence of Cs2CO3 as base (10 mol %) under hydrogen‐borrowing conditions. Using 2‐aminobenzyl alcohol as alkylation reagent allows for the “green” synthesis of quinoline derivatives. 相似文献
20.
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