共查询到20条相似文献,搜索用时 15 毫秒
1.
The Synthesis of Benzimidazoles and Quinoxalines from Aromatic Diamines and Alcohols by Iridium‐Catalyzed Acceptorless Dehydrogenative Alkylation 下载免费PDF全文
Toni Hille Dr. Torsten Irrgang Prof. Dr. Rhett Kempe 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5569-5572
Benzimidazoles and quinoxalines are important N‐heteroaromatics with many applications in pharmaceutical and chemical industry. Here, the synthesis of both classes of compounds starting from aromatic diamines and alcohols (benzimidazoles) or diols (quinoxalines) is reported. The reactions proceed through acceptorless dehydrogenative condensation steps. Water and two equivalents of hydrogen are liberated in the course of the reactions. An Ir complex stabilized by the tridentate P^N^P ligand N2,N6‐bis(di‐isopropylphosphino)pyridine‐2,6‐diamine revealed the highest catalytic activity for both reactions. 相似文献
2.
Shintaro Hatanaka Yasushi Obora Dr. Yasutaka Ishii Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(6):1883-1888
A novel iridium‐catalyzed intermolecular coupling reaction of primary alcohols or aldehydes with 2‐alkynes was successfully achieved with high regioselectivity to give hydroacylation products such as α,β‐unsaturated ketones in good yields. The mechanistic investigation of the reaction strongly indicated that the coupling proceeds through the initial formation of homoallylic alcohols followed by dehydrogenation to β,γ‐unsatutated ketones and then isomerisation, which leads to the hydroacylation products. 相似文献
3.
4.
Luca Mantilli David Gérard Sonya Torche Céline Besnard Dr. Clément Mazet Dr. 《Angewandte Chemie (International ed. in English)》2009,48(28):5143-5147
Nothing to sm(Ir)k at : Under appropriate reaction conditions, iridium hydride catalysts promote the isomerization of primary allylic alcohols. The best catalysts, like (R)‐ 1 (P green, O red, N blue, Ir yellow), deliver the desired chiral aldehydes with excellent enantioselectivity and good yields. Mechanistic hypotheses have been developed on the basis of preliminary investigations.
5.
Prof. Süleyman Gülcemal Prof. Derya Gülcemal Dr. George F. S. Whitehead Prof. Jianliang Xiao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(30):10513-10522
A series of new IrIII complexes with carbene ligands that contain a range of benzyl wingtip groups have been prepared and fully characterised by NMR spectroscopy, HRMS, elemental analysis and X‐ray diffraction. All the complexes were active in the acceptorless dehydrogenation of alcohol substrates in 2,2,2‐trifluoroethanol to give the corresponding carbonyl compounds. The most active complex bore an electron‐rich carbene ligand; this complex was used to catalyse the highly efficient and chemoselective dehydrogenation of a wide range of secondary alcohols to their respective ketones, with turnover numbers up to 1660. Mechanistic studies suggested that the turnover of the dehydrogenation reaction is limited by the H2‐formation step. 相似文献
6.
Iridium‐Catalyzed Intermolecular Dehydrogenative Silylation of Polycyclic Aromatic Compounds without Directing Groups 下载免费PDF全文
Dr. Masahito Murai Keishi Takami Prof. Dr. Kazuhiko Takai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4566-4570
This study describes the iridium‐catalyzed intermolecular dehydrogenative silylation of C(sp2)?H bonds of polycyclic aromatic compounds without directing groups. The reaction produced various arylsilanes through both Si?H and C?H bond activation, with hydrogen as the sole byproduct. Reactivity was affected by the electronic nature of the aromatic compounds, and silylation of electron‐deficient and polycyclic aromatic compounds proceeded efficiently. Site‐selectivity was controlled predominantly by steric factors. Therefore, the current functionalization proceeded with opposite chemo‐ and site‐selectivity compared to that observed for general electrophilic functionalization of aromatic compounds. 相似文献
7.
Iridium‐Catalyzed Asymmetric Hydrogenation of 3,3‐Disubstituted Allylic Alcohols in Ethereal Solvents 下载免费PDF全文
Maurizio Bernasconi Vincenzo Ramella Dr. Paolo Tosatti Prof. Dr. Andreas Pfaltz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(9):2440-2444
Ir‐phosphinomethyl‐oxazoline complexes have been identified as efficient, highly enantioselective catalysts for the asymmetric hydrogenation of 3,3‐disubstituted allylic alcohols and related homoallylic alcohols. In contrast to other N,P ligand complexes, which require weakly coordinating solvents, such as dichloromethane, these catalysts perform well in more ecofriendly THF or 2‐MeTHF. Their synthetic potential was demonstrated with the formal total synthesis of four bisabolane sesquiterpenes. 相似文献
8.
Manganese‐Catalyzed Dehydrogenative Alkylation or α‐Olefination of Alkyl‐Substituted N‐Heteroarenes with Alcohols 下载免费PDF全文
Dr. Guoying Zhang Dr. Torsten Irrgang Thomas Dietel Fabian Kallmeier Prof. Dr. Rhett Kempe 《Angewandte Chemie (International ed. in English)》2018,57(29):9131-9135
Catalysis with earth‐abundant transition metals is an option to help save our rare noble‐metal resources and is especially interesting when novel reactivity or selectivity patterns are observed. We report here on a novel reaction, namely the dehydrogenative alkylation or α‐olefination of alkyl‐substituted N‐heteroarenes with alcohols. Manganese complexes developed in our laboratory catalyze the reaction with high efficiency whereas iron and cobalt complexes stabilized by the same ligands are essentially inactive. Hydrogen is liberated during the reaction, and bromine and iodine functional groups as well as olefins are tolerated. A variety of alkyl‐substituted N‐heteroarenes can be functionalized, and benzylic and aliphatic alcohols undergo the reaction. 相似文献
9.
10.
Luca Mantilli David Gérard Sonya Torche Dr. Céline Besnard Dr. Clément Mazet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(42):12736-12745
An improved generation of chiral cationic iridium catalysts for the asymmetric isomerization of primary allylic alcohols is disclosed. The design of these air‐stable complexes relied on the preliminary mechanistic information available, and on Charton analyses using two preceding generations of iridium catalysts developed for this highly challenging transformation. Sterically unbiased chiral aldehydes that were not accessible previously have been obtained with high levels of enantioselectivity, thus validating the initial hypothesis regarding the selected ligand‐design elements. A rationale for the high enantioselectivities achieved in most cases is also presented. 相似文献
11.
12.
13.
《中国化学》2018,36(3):233-240
The I2 catalyzed highly selective oxidative condensation of cyclohexenones and alcohols for the synthesis of aryl alkyl ethers has been described. DMSO is employed as the mild terminal oxidant. This novel methodology offers a metal‐free reaction condition, operational simplicity and broad substrate scope to afford valuable products from inexpensive reagents. Various meta‐substituted aromatic ethers which are hardly synthesized from the reported methods requiring meta‐substituted phenols, are efficiently prepared by the present protocol. 相似文献
14.
15.
16.
《Angewandte Chemie (International ed. in English)》2017,56(12):3237-3241
An Ir‐catalyzed intermolecular asymmetric dearomatization reaction of β‐naphthols with allyl alcohols or allyl ethers was developed. When an iridium catalyst generated from [Ir(COD)Cl]2 (COD=cyclooctadiene) and a chiral P/olefin ligand is employed, highly functionalized β‐naphthalenone compounds bearing an all‐carbon‐substituted quaternary chiral center were obtained in up to 92 % yield and 98 % ee . The direct utilization of allyl alcohols as electrophiles represents an improvement from the viewpoint of atom economy. Allyl ethers were found to undergo asymmetric allylic substitution reaction under Ir catalysis for the first time. The diverse transformations of the dearomatized product to various motifs render this method attractive. 相似文献
17.
Johan Hygum Dam Dr. Gyorgyi Osztrovszky Lars Ulrik Nordstrøm Dr. Robert Madsen Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6820-6827
The direct synthesis of amides from alcohols and amines is described with the simultaneous liberation of dihydrogen. The reaction does not require any stoichiometric additives or hydrogen acceptors and is catalyzed by ruthenium N‐heterocyclic carbene complexes. Three different catalyst systems are presented that all employ 1,3‐diisopropylimidazol‐2‐ylidene (IiPr) as the carbene ligand. In addition, potassium tert‐butoxide and a tricycloalkylphosphine are required for the amidation to proceed. In the first system, the active catalyst is generated in situ from [RuCl2(cod)] (cod=1,5‐cyclooctadiene), 1,3‐diisopropylimidazolium chloride, tricyclopentylphosphonium tetrafluoroborate, and base. The second system uses the complex [RuCl2(IiPr)(p‐cymene)] together with tricyclohexylphosphine and base, whereas the third system employs the Hoveyda–Grubbs 1st‐generation metathesis catalyst together with 1,3‐diisopropylimidazolium chloride and base. A range of different primary alcohols and amines have been coupled in the presence of the three catalyst systems to afford the corresponding amides in moderate to excellent yields. The best results are obtained with sterically unhindered alcohols and amines. The three catalyst systems do not show any significant differences in reactivity, which indicates that the same catalytically active species is operating. The reaction is believed to proceed by initial dehydrogenation of the primary alcohol to the aldehyde that stays coordinated to ruthenium and is not released into the reaction mixture. Addition of the amine forms the hemiaminal that undergoes dehydrogenation to the amide. A catalytic cycle is proposed with the {(IiPr)RuII} species as the catalytically active components. 相似文献
18.
《Angewandte Chemie (International ed. in English)》2017,56(1):371-374
New reactions that convert alcohols into important classes of compounds are becoming increasingly important as their development contributes to the conservation of our fossil carbon feedstock and the reduction of CO2 emissions. Two key catalytic alcohol conversion concepts are borrowing hydrogen or hydrogen autotransfer and acceptorless dehydrogenative condensation. Herein, we combined both concepts to synthesize meta ‐functionalized pyridines. First, diols and amines were linked to β‐amino alcohols, which can then undergo a selective dehydrogenative heterocondensation with γ‐amino alcohols. Iridium catalysts stabilized by PN5P pincer ligands that were developed in our laboratory mediate the reactions most efficiently. All of the 3‐aminopyridines that we describe in this paper have been synthesized for the first time, emphasizing the degree of innovation of this method and the problems associated with the synthesis of such meta ‐functionalized pyridines. 相似文献
19.
Benoît Blank Stefan Michlik Rhett Kempe Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(15):3790-3799
Selective amine alkylation : A P,N‐ligand‐stabilized iridium complex has been used as an efficient catalyst for the alkylation of (hetero)aromatic amines with alcohols at mild reaction temperatures and catalyst loadings as low as 0.1 mol % Ir (see scheme). The excellent selectivity of the catalyst for monoalkylation of the amine function has also been exploited for the N,N′‐dialkylation of diamines in both symmetric and nonsymmetric fashions.
20.
Ritwika Ray Shubhadeep Chandra Prof. Debabrata Maiti Prof. Goutam Kumar Lahiri 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(26):8814-8822
Oxidative transformations utilizing molecular oxygen (O2) as the stoichiometric oxidant are of paramount importance in organic synthesis from ecological and economical perspectives. Alcohol oxidation reactions that employ O2 are scarce in homogeneous catalysis and the efficacy of such systems has been constrained by limited substrate scope (most involve secondary alcohol oxidation) or practical factors, such as the need for an excess of base or an additive. Catalytic systems employing O2 as the “primary” oxidant, in the absence of any additive, are rare. A solution to this longstanding issue is offered by the development of an efficient ruthenium‐catalyzed oxidation protocol, which enables smooth oxidation of a wide variety of primary, as well as secondary benzylic, allylic, heterocyclic, and aliphatic, alcohols with molecular oxygen as the primary oxidant and without any base or hydrogen‐ or electron‐transfer agents. Most importantly, a high degree of selectivity during alcohol oxidation has been predicted for complex settings. Preliminary mechanistic studies including 18O labeling established the in situ formation of an oxo–ruthenium intermediate as the active catalytic species in the cycle and involvement of a two‐electron hydride transfer in the rate‐limiting step. 相似文献