Meetings by month
Hongli Bao, Xiangbing Qi, and Uttam K. Tambar*
The first Pd-catalyzed enantioselective [2,3]-rearrangement of allylic amine N-oxides is described, which formally represents an asymmetric Meisenheimer rearrangement. The mild reaction conditions enable the synthesis of chiral nonracemic aliphatic allylic alcohol derivatives with reactive functional groups. On the basis of preliminary studies, a cyclization-mediated mechanism is proposed.
Efficient Iron/Copper-Cocatalyzed O-Arylation of Phenols with Bromoarenes
Xiaoyan Liu, Songlin Zhang
Low catalytic amount CuI and Fe(acac)3 were found to effectively promote the C-O cross-coupling reaction in the presence of K2CO3 as the base. A serious of diaryl ethers with different substitutents can be synthesized in good to excellent yields. This efficient and economic method is attractive for applications on an industrial scale.
Enantioselective Synthesis of Biphenols from 1,4-Diketones by Traceless Central-to-Axial Chirality Exchange
Fenghai Guo, Leah C. Konkol, and Regan J. Thomson
J. Am. Chem. Soc., 2011, 133, 18–20
A method for the enantioselective synthesis of biphenols from readily prepared 1,4-diketones is reported. Key to the success of this method is the highly selective transfer of central to axial chirality during a double aromatization event triggered by BF3·OEt2. On the basis of X-ray crystallographic data, a stereochemical model for this chirality exchange process is put forth.
Rhodium (I)-Catalyzed Direct Carboxylation of Arenes with CO2 via Chelation-Assisted C-H Bond Activation
Hajime Mizuno, Jun Takaya, and Nobuharu Iwasawa
Rh-catalyzed direct carboxylation of unactivated aryl C−H bond under atmospheric pressure of carbon dioxide was realized via chelation-assisted C−H activation for the first time. Variously substituted and functionalized 2-arylpyridines and 1-arylpyrazoles underwent the carboxylation in the presence of the rhodium catalyst and a stoichiometric methylating reagent, AlMe2(OMe), to give carboxylated products in good yields. The catalysis is proposed to consist of methylrhodium(I) species as the key intermediate, which undergoes C−H activation to afford rhodium(III), followed by reductive elimination of methane to give nucleophilic arylrhodium(I). This approach demonstrates promising application of C−H bond activation strategy in the field of carbon dioxide fixation.
A General Procedure for the Synthesis of Enones via Gold-Catalyzed Meyer−Schuster Rearrangement of Propargylic Alcohols at Room Temperature
Matthew N. Pennell, Matthew G. Unthank, Peter Turner, and Tom D. Sheppard
Meyer−Schuster rearrangements of propargylic alcohols take place readily at room temperature in toluene with 1−2 mol % PPh3AuNTf2, in the presence of 0.2 equiv of 4-methoxyphenylboronic acid or 1 equiv of methanol. Good to excellent yields of enones can be obtained from secondary and tertiary alcohols, with high selectivity for the E-alkene in most cases. A one-pot procedure for the conversion of primary propargylic alcohols into β-arylketones was also developed, via Meyer-Schuster rearrangement followed by Pd-catalayzed addition of a boronic acid.http://pubs.acs.org/doi/abs/10.1021/jo102263t
J. Org. Chem., Article ASAP
The structure of the alkylzinc−tetramethylethyl-enediamine (TMEDA) cluster cation 3 has been determined in the gas phase by a combination of tandem mass spectrometry, infrared multiphoton dissociation (IRMPD) spectroscopy, and DFT calculations. Both sets of experimental results establish the existence of a strongly stabilizing interaction of TMEDA with the zinc cation. High-level DFT calculations on the alkylzinc−TMEDA cluster cation 3allowed the identification of two low energy conformers, each featuring a four-coordinate zinc atom with a bidentate TMEDA ligand, and internal coordination from the carbonyl group of the Boc group to zinc. The experimental IRMPD spectrum is reproduced with an appropriately weighted combination of the IR spectra of the two conformers identified by theory. DFT calculations on the structure of the alkylzinc halide 2 with coordinated TMEDA using the PCM model of water solvent suggest that TMEDA can promote ionization of the zinc−iodine bond in organozinc iodides under aqueous conditions, providing a credible explanation for the role of TMEDA in stabilizing the carbon−zinc bond. Reaction of the serine-derived iodide 1 with aryl iodides “on water”, promoted by nano zinc in the presence of PdCl2(Amphos)2 (5 mol %) and TMEDA, leads to the formation of protected phenylalanine derivatives 4 in reasonable yields. In the case of ortho-substituted aryl iodides and aryl iodides that are solids at room temperature, conducting the reaction at 65 °C gives improved results. In all cases, the product 5 of reductive dimerization of the iodide 1 is also isolated.
J. Am. Chem. Soc., Article ASAP
The highly enantioselective catalytic asymmetric addition of aryl and alkenylboronic acids toN-benzylnicotinate salt 1 is described. The dihydropyridine 2 reaction products can be converted to synthetically useful piperidines. Application of the methodology to the preparation of enantioenriched quaternary chiral centers is also discussed.
CuI-Nanoparticles-Catalyzed Selective Synthesis of Phenols, Anilines, and Thiophenols from Aryl Halides in Aqueous Solution
Hua-Jian Xu*†‡, Yu-Feng Liang†, Zhen-Ya Cai†, Hong-Xia Qi†, Chun-Yan Yang†, and Yi-Si Feng*†‡
† School of Chemical Engineering, Hefei University of Technology, Hefei 230009, People's Republic of China
‡ Anhui Key Laboratory of Controllable Chemistry Reaction & Material Chemical Engineering, Hefei 230009, People's Republic of China
J. Org. Chem., Article ASAP
Publication Date (Web): February 28, 2011
Copyright © 2011 American Chemical Society
CuI-nanoparticles-catalyzed selective synthesis of phenols, anilines, and thiophenols from aryl halides was developed in the absence of both ligands and organic solvents. Anilines were formed selectively with ammonia competing with hydroxylation and thiophenols were generated selectively with sulfur powder after subsequent reduction competing with hydroxylation and amination.
Nickel-Catalyzed Cross-Coupling of Aryl Phosphates with Arylboronic Acids
Hu Chen, Zhongbin Huang, Xiaoming Hu, Guo Tang, Pengxiang Xu, Yufen Zhao, and Chien-Hong Cheng
The Suzuki−Miyaura cross-coupling of aryl phosphates using Ni(PCy3)2Cl2 as an inexpensive, bench-stable catalyst is described. Broad substrate scope and high efficiency are demonstrated by the syntheses of more than 40 biaryls and by constructing complex organic molecules. The poor reactivity of aryl phosphates relative to aryl halides is successfully employed to construct polyarenes by selective cross-coupling using Pd and Ni catalysts.
Double C−H Activation: The Palladium-Catalyzed Direct C-Arylation of Xanthines with Arenes
Chandi C. Malakar, Dietmar Schmidt, J rgen Conrad, and Uwe Beifuss
The novel Pd-catalyzed C(sp2)−H/C(sp2)−H cross-coupling of unactivated xanthines with unactivated arenes utilizing a combination of Ag(I) and O2 as oxidants exclusively yields C-8 arylated xanthines in a single synthetic operation.
Org. Lett., 2011, 13 (6), pp 1378–1381
Dante Rotili, Mikael Altun, Refaat B. Hamed, Christoph Loenarz, Armin Thalhammer, Richard J. Hopkinson, Ya-Min Tian, Peter J. Ratcliffe, Antonello Mai, Benedikt M. Kessler and Christopher J. Schofield
Photoactivated cross-linking of peptides to proteins is a useful strategy for identifying enzyme–substrate and protein–protein interactions in cell lysates as demonstrated by studies on the human hypoxia inducible factor system.
Marcos J. Lo Fiego, Gustavo F. Silbestri, Alicia B. Chopa§, and Mar a T. Lockhart*
Instituto de Qu mica del Sur (CONICET − UNS), Departamento de Qu mica, Universidad Nacional del Sur, Avenida Alem 1253, Bah a Blanca, B8000CPB, Argentina
Bulky arylstannanes and bulky aroyl chlorides are good reaction partners for the synthesis of two-, three-, and even four-ortho-substituted benzophenones, in good to excellent isolated yields (47−91%). Three simple and direct routes, with differential advantages, are proposed: (i) a catalyst-free protocol, in o-dichlorobenzene (ODCB) at 180 °C; (ii) a room temperature protocol, using AlCl3 (0.5 equiv), in dichloromethane (DCM); and (iii) a solvent-free, indium-promoted procedure. A radical mechanism is proposed for the indium-mediated reactions.
Andrew J. A. Watson†, Aoife C. Maxwell‡, and Jonathan M. J. Williams*†
† Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
‡ GlaxoSmithKline Research and Development, Gunnels Wood Road, Stevenage SG1 2NY, U.K.
Application of microwave heating to the Borrowing Hydrogen strategy to form C−N bonds from alcohols and amines is presented, removing the need for solvent and reducing the reaction times while still yielding results comparable with those using thermal heating.
A Silver-Mediated One-Step Synthesis of Oxazoles
Dougal J. Ritson, Christian Spiteri, and John E. Moses
A silver-mediated one-step procedure to 2,4-disubstituted and 2,4,5-trisubstituted oxazoles has been developed. The method is complementary to existing technologies, yet provides advantages with regard to simplicity, efficiency, and performance. The silver product can be readily recycled, thus minimizing waste.
Three-Component Synthesis of Cyclic Enaminones via Ketene Cyclization
Hajime Seki and Gunda I. Georg
Cyclic six-membered enaminones were synthesized from three components (bromodiazoacetone, primary amine, and alkyne) in high yields via aza-Michael addition, Wolff rearrangement, and nucleophilic ketene cyclization.
Charlotte Hollingworth, Dr. Amaruka Hazari, Matthew N. Hopkinson, Dr. Matthew Tredwell, Elena Benedetto, Dr. Mickael Huiban, Prof. Antony D. Gee, Dr. John M. Brown, Prof. Véronique Gouverneur
Mild and rapid: The title reaction is presented and its applicability to 18F radiolabeling is demonstrated (see scheme; TBAF=tetra-n-butylammonium fluoride, THF=tetrahydrofuran, dba=dibenzylideneacetone). The use of p-nitrobenzoate as the leaving group is significant to the success of this catalytic organometallic fluorination process. A range of allylic fluorides were synthesized by this method.
Magnus Rueping* and Alejandro Parra
Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52074 Aachen, Germany
(E)-β-Bromonitrostyrenes react with enaminones in water to afford pyrroles in excellent yields. The domino reaction constitutes a new, mild, and environmentally benign process for the fast and efficient synthesis of diverse pyrroles.
Mitsutaka Iwata,† Ryo Yazaki,†,‡ I-Hon Chen,† Devarajulu Sureshkumar,† Naoya Kumagai,*,† and Masakatsu Shibasaki*,†
A direct catalytic asymmetric aldol reaction of thioamides using a soft Lewis acid/hard Brønsted base cooperative catalyst comprising (R,R)-Ph-BPE/[Cu(CH3CN)4]PF6/LiOAr is described. Exclusive enolate generation from thioacetamides through a soft−soft interaction with the soft Lewis acid allowed for a direct aldol reaction to α-nonbranched aliphatic aldehydes, which are usually susceptible to self-condensation under conventional basic conditions. A hard Lewis basic phosphine oxide has emerged as an effective additive to constitute a highly active ternary soft Lewis acid/hard Brønsted base/hard Lewis base cooperative catalyst, enabling a direct enantio- and diastereoselective aldol reaction of thiopropionamides. Strict control of the amount of the hard Lewis base was essential to drive the catalytic cycle efficiently with a minimized retro-aldol pathway, affording syn-aldol products with high stereoselectivity. Divergent transformation of the thioamide functionality is an obvious merit of the present aldol methodology, allowing for a facile transformation of the aldol product into the corresponding aldehyde, ketone, amide, amine, and ketoester. An aldehyde derived from the direct aldol reaction was subjected to a second direct aldol reaction, which proceeded in a catalyst-controlled manner to provide 1,3-diols with high stereoselectivity.
Copper-Mediated Coupling of 1,1-Dibromo-1-alkenes with Imidazoles: A General Method for the Synthesis of N-Alkynylimidazoles
Mangang Wang, Jun Wu, and Zhicai Shang
A Cu(I)-catalyzed cross-coupling reaction leading to the synthesis of N-alkynylheteroarenes from 1,1-dibromo-1-alkenes is described. Generally superior yields and functional group tolerance were obtained with TMEDA as ligand using imidazole and benzimidazole substrates in dioxane.
Tobias Thaler, Li-Na Guo, Andreas K. Steib, Mihai Raducan, Konstantin Karaghiosoff, Peter Mayer, and Paul Knochel*
Sulfoxidealkene hybrids are introduced as a new class of chiral heterodentate ligands for the HayashiMiyaura reaction. The synthesis of these ligands was achieved without the use of protecting groups. A chiral resolution was performed via simple column-chromatographic separation of the diastereomeric ligands. Both diastereomers proved to be excellent ligands in Rh-catalyzed 1,4-addition reactions, furnishing chiral products with high enantioselectivities and, remarkably, opposite stereoconfigurations.
Enantioselective Synthesis of Highly Substituted Furans by a Copper(II)-Catalyzed CycloisomerizationIndole Addition Reaction
Vivek Rauniyar, Z. Jane Wang, Heather E. Burks, and F. Dean Toste*
ABSTRACT: A catalytic enantioselective reaction based on a copper(II) catalyst strictly containing chiral anionic ligands is described. In the present work, copper(II)_phosphate catalyst promotes the intramolecular heterocyclization of 2-(1-alkynyl)-2-alkene-1-ones and facilitates high levels of enantioselectivity in the subsequent nucleophile attack. Mechanistic studies suggest that formation of a copper(II)_ indole species is important for catalysis.
Simple, Stable, and Easily Accessible Well-Defined CuCF3 Aromatic Trifluoromethylating Agents
Direct Michael Addition of Alkenes via a Cobalt-Dinitrosyl Mediated Vinylic C–H Functionalization Reaction
ABSTRACT: We report a one-pot, direct CH functionalization reaction of alkenes mediated by [CpCo(NO)2]. All intermediates in the proposed reaction sequence have been characterized. A variety of Michael acceptors can be utilized with the one-pot procedure to give the desired cyclic tetraalkylsubstituted, γ,δ-unsaturated compounds in good yields. We also provide a preliminary result for catalytic turnover in both base and [CpCo(NO)2].
"On water" sp3-sp2 cross-couplings between benzylic and alkenyl halides
Valeria Krasovskaya, Arkady Krasovskiy, Anish Bhattacharjya and Bruce H. Lipshutz
Chem. Commun., 2011, 47, 5717-5719
Organic-solvent-free cross-couplings between benzylic and alkenyl halides have been developed. Various alkenyl halides can be efficiently benzylated by combining the precursor halides in the presence of Zn dust and a Pd catalyst at room temperature, in water as the only medium.
Kim L. Jensen, Gustav Dickmeiss, Bjarke S. Donslund, Pernille H. Poulsen, and Karl Anker Jørgensen*
Center for Catalysis, Aarhus University, 8000 Aarhus C, Denmark
Org. Lett., Article ASAP
The sequential use of Cu-catalyzed asymmetric allylic alkylation, olefin cross-metathesis, and Ir-catalyzed asymmetric allylic amination allows the concise, stereodivergent synthesis of complex chiral amines with complete regiocontrol and good diastereoselectivity, exemplified by the synthesis of a pair of diastereoisomeric unnatural branched amino acid derivatives.
Combined Carbometalation–Zinc Homologation–Allylation Reactions as a New Approach for Alkoxyallylation of Aldehydes
The Mallat Family Laboratory of Organic Chemistry, Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel, and Laboratory for X-ray Analysis, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel
Org. Lett., Article ASAP
Krishna Kanta Ghosh, Hyung-Ho Ha, Nam-Young Kang, Yogeswari Chandran and Young-Tae Chang
Chem. Commun., 2011, 47, 7488-7490
We report the first solid phase synthesis of a xanthone library CX and its application to embryonic stem cell probe development. The CX library was further derivatised with an activated ester resin to provide an acetylated CX (CXAC) library. Screening of these libraries led to the discovery of a novel fluorescent mESC probe, CDb8.
Palladium-Catalyzed Minisci Reaction with Simple Alcohols
Camille A. Correia, Luo Yang, and Chao-Jun Li
A palladium-catalyzed coupling of N-heterocycles with simple alcohols was achieved. The reaction is initiated by peroxide and does not require the use of stoichiometric acid for activation of the heterocycle.
Synthesis of gem-Difluorinated Cyclopropanes and Cyclopropenes: Trifluoromethyltrimethylsilane as a Difluorocarbene Source
Fei Wang, Tao Luo, Jinbo Hu, Ying Wang, Hema S. Krishnan, Parag V. Jog, Somesh K. Ganesh, G. K. Surya Prakash2, George A. Olah
Highly versatile: The Ruppert–Prakash reagent (Me3SiCF3) can be an efficient source of difluorocarbene. By varying the nonmetallic initiator that is used (F− at lower temperatures and I− at higher temperatures), a range of structurally diverse alkenes and alkynes can be converted into the corresponding gem-difluorinated cyclopropanes and cyclopropenes in good yields (see scheme)
γ-Selective Cross-Coupling of Allylic Silanolate Salts with Aromatic Bromides Using Trialkylphosphonium Tetrafluoroborate Salts Prepared Directly from Phosphine•Borane Adducts
Scott E. Denmark and Nathan S. Werner
The γ-selective, palladium-catalyzed cross-coupling of sodium (Z)-2-butenyldiethylsilanolate with a variety of aromatic bromides is reported. The protocol provides high yields (73–94%) and site selectivity (γ/α, 25:1 → > 99:1) in the coupling of electron-rich, electron-poor, sterically hindered, and heteroaromatic bromides. The use of a configurationally homogeneous (Z)-silanolate, nontransferable ethyl groups, and a sterically bulky trialkylphosphonium tetrafluoroborate salt (t-BuCy2PH+BF4–) prepared directly from the corresponding air-stable phosphine•borane adduct are critical to the success of the method.
Synthesis of 2,4,6-trisubstituted pyridines via an olefin cross-metathesis/Heck–cyclisation–elimination sequence
Timothy J. Donohoe, John F. Bower, David B. Baker, José A. Basutto, Louis K. M. Chan and Peter Gallagher
Heck reactions were performed on α,β-unsaturated-δ-sulfonamido intermediates, derived from cross metathesis, to allow the instalment of substituents at the β position. Subsequent one-pot cyclisation/elimination provides an operationally simple, catalytic and convergent synthesis of 2,4,6-trisubstituted pyridines. paper
Dr. Takeshi Yamamoto1, Yuto Akai1, Dr. Yuuya Nagata1, Prof. Dr. Michinori Suginome1,2,*
Taking a new turn: An asymmetric Suzuki–Miyaura coupling of 1-bromo-2-naphthalenephosphonic esters with o-methyl-substituted phenylboronic acids proceeds with high enantioselectivity in the presence of high-molecular-weight helically chiral polyquinoxaline-based phosphines (PQXphos) bearing pendant diarylphosphino groups
Palladium-Catalyzed Amination of Allyl Alcohols
Raju Ghosh and Amitabha Sarkar
An efficient catalytic amination of aryl-substituted allylic alcohols has been developed. The complex [(η3-allyl)PdCl]2 modified by a bis phosphine ligand, L, has been used as catalyst in the reaction that afforded a wide range of allyl amines in good to excellent yield under mild conditions.
An Enantioselective, Intermolecular α-Arylation of Ester Enolates To Form Tertiary Stereocenters
Zhiyan Huang, Zheng Liu, and Jianrong (Steve) Zhou
In transition-metal catalyzed, asymmetric α-arylation of carbonyl compounds, formation of tertiary centers with high enantioselectivity is a longstanding problem, due to easy enolization of the monoarylation products. Herein, we report such examples using a palladium catalyst supported by a new, (R)-H8-BINOL-derived monophosphine. Silyl ketene acetals, together with a weakly basic activator, were used as equivalents of ester anions, and they reacted smoothly with aryl triflates in excellent enantiomeric excess (ee). The usefulness of the reaction was demonstrated in a gram-scale synthesis of (S)-Naproxen in 92% ee.
C–H Arylation of Pyridines: High Regioselectivity as a Consequence of the Electronic Character of C–H Bonds and Heteroarene Ring
Pengfei Guo, Jung Min Joo, Souvik Rakshit, and Dalibor Sames
We report a new catalytic protocol for highly selective C–H arylation of pyridines containing common and synthetically versatile electron-withdrawing substituents (NO2, CN, F and Cl). The new protocol expands the scope of catalytic azine functionalization as the excellent regioselectivity at the 3- and 4-positions well complements the existing methods for C–H arylation and Ir-catalyzed borylation, as well as classical functionalization of pyridines. Another important feature of the new method is its flexibility to adapt to challenging substrates by a simple modification of the carboxylic acid ligand or the use of silver salts. The regioselectivity can be rationalized on the basis of the key electronic effects (repulsion between the nitrogen lone pair and polarized C–Pd bond at C2-/C6-positions and acidity of the C–H bond) in combination with steric effects (sensitivity to bulky substituents).
Synthesis of Phenanthridinones from N-Methoxybenzamides and Arenes by Multiple Palladium-Catalyzed C H Activation Steps at Room Temperature
Jaganathan Karthikeyan and Chien-Hong Cheng
Many steps make light work: Substituted phenanthridinones can be obtained with high regioselectivity and in very good yields by palladium-catalyzed cyclization reactions of N-methoxybenzamides with arenes (see scheme). The reaction proceeds through multiple oxidative C-H activation and C-C/C-N formation steps in one pot at room temperature, and thus provides a simple method for generating bioactive phenanthridinones. DOI: 10.1002/anie.201104311
Using Nazarov Electrocyclization to Stage Chemoselective [1,2]-Migrations: Stereoselective Synthesis of Functionalized Cyclopentenones †
Dr. David Lebœuf1, Dr. Jie Huang1, Prof. Vincent Gandon2, Prof. Alison J. Frontier1
Highly functionalized cyclopentenones have been prepared stereospecifically through a chemoselective copper(II)-mediated Nazarov/Wagner–Meerwein rearrangement sequence. After the initial 4π electrocyclization, this reaction involves two sequential [1,2]-migrations depending upon both migratory ability and steric bulk of the substituents at C1 and C5 (see scheme). The proposed mechanism of the reaction is supported by DFT studies.
Palladium-Catalysed Coupling of Arene C-H Bonds with Methyl- and Arylboron Reagents Assisted by the Removalble 2-Pyridylsulfinyl Group
José A. Romero-Revilla, Alfonso Garcı́a-Rubia, Ramón Goméz Arrayás*, M. Ángeles Fernández-Ibáñez*, and Juan C. Carretero*
The PdII-catalyzed direct coupling of arene C–H bonds with organoboron reagents assisted by the 2-pyridylsulfinyl group is reported. Methylboronic acid and arylboronic acid neopentyl esters proved to be efficient coupling partners, furnishing methylated arenes and biaryl products in moderate to good yields. The 2-pyridylsulfinyl group can be easily removed to provide the free biaryls. The essential role of the 2-pyridyl unit in stabilizing the cyclopalladation complex was demonstrated by X-ray diffraction analysis of the palladacycle intermediate.
Palladium-Catalysed Carbohalogenation: Bromide to Iodide Exchange and Domino Processes
Stephen G. Newman, Jennifer K. Howell, Norman Nicolaus and Mark Lautens*
Aryl bromides have been used to prepare a variety of nitrogen- and oxygen-containing heterocycles featuring new carbon–carbon and carbon–iodine bonds. This palladium-catalyzed carbohalogenation requires potassium iodide for the reaction to proceed in high yields. Additionally, the first examples of domino carbohalogenation reactions have been demonstrated using both aryl iodide and aryl bromide starting materials. Complex products with multiple rings and stereogenic centers are generated in excellent yields with moderate to excellent diastereoselectivities.
Copper-Catalyzed Intramolecular Hydroalkoxylation of α-(1-Hydroxy-1-alkyl- and -aryl)methylallenoates by a 5-Endo Mode for Preparation of 2-Alkyl- and 2-Aryl-2,5-dihydrofurans
Sanghyuck Kim and Phil Ho Lee
Ethyl α-(1-hydroxy-1-alkyl)methylallenoates and α-(1-hydroxy-1-aryl)methylallenoates containing not only electron-donating groups but also an electron-withdrawing group on the aryl group at the α-position have been shown to undergo an efficient and selective copper-catalyzed intramolecular hydroalkoxylation to give functionalized 3-ethoxycarbonyl-2-alkyl- and -aryl-2,5-dihydrofurans in good to excellent yields through a 5-endo mode. DOI: 10.1021/jo2018125
Enantioselective Bromocyclization of Olefins Catalyzed by Chiral Phosphoric Acid
Deshun Huang, Haining Wang, Fazhen Xue, Huan Guan, Lijun Li, Xianyou Peng, and Yian Shi
A chiral phosphoric acid catalyzed enantioselective bromocyclization of olefins is described. Various cis-, trans-, or trisubstituted γ-hydroxy-alkenes and γ-amino-alkenes can cyclize under the reaction conditions to give optically active 2-substituted tetrahydrofurans and tetrahydropyrroles in up to 91% ee. DOI: 10.1021/ol202527g
Prof. Eiji Shirakawa, Yumi Hayashi, Ken-ichi Itoh, Ryo Watabe, Nanase Uchiyama, Wataru Konagaya, Seiji Masui, Prof. Tamio Hayashi
This work has been supported financially in part by Grant-in-Aids for Scientific Research on Innovative Areas “Molecular Activation Directed toward Straightforward Synthesis” (23105521 to E.S.) and by the Global COE Program “Integrated Materials Science” from the Ministry of Education, Culture, Sports, Science and Technology of Japan. N.U. thanks the JSPS for a Research Fellowship for Young Scientists. We are grateful to Yuki Yamamoto, Mitsuru Harada, Dr. Kenji Kitayama, and Ikuo Takahashi (Daicel Chemical Industries, Ltd.) for ICP analysis.
Scott E. Denmark and Matthew T. Burk
A binary catalyst system for the enantioselective bromocycloetherification of 5-arylpentenols is described. The combination of an achiral Lewis base and a chiral Brønsted acid affords good enantioselectivities for the cyclization of Z configured 5-arylpentenols to form bromomethyltetrahydrofurans. The constitutional site selectivity is highly dependent upon the aromatic substituent and the configuration of the double bond.