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1.
Gansäuer A Knebel K Kube C van Gastel M Cangönül A Daasbjerg K Hangele T Hülsen M Dolg M Friedrich J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(9):2591-2599
The mechanism of catalytic 4-exo cyclizations without gem-dialkyl substitution was investigated by a comparison of cyclic voltammetry, EPR, and computational studies with previously published synthetic results. The most active catalyst is a super-unsaturated 13-electron titanocene(III) complex that is formed by supramolecular activation through hydrogen bonding. The template catalyst binds radicals via a two-point binding that is mandatory for the success of the 4-exo cyclization. The computational investigations revealed that formation of the observed trans-cyclobutane product is not possible from the most stable substrate radical. Instead, the most stable product is formed with the lowest energy of activation from a disfavored substrate in a Curtin-Hammett related scenario. 相似文献
2.
Dr. Genping Huang Bing Cheng Liang Xu Prof. Dr. Yahong Li Prof. Dr. Yuanzhi Xia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5401-5415
A comprehensive mechanistic study of the InCl3‐, AuCl‐, and PtCl2‐catalyzed cycloisomerization of the 2‐(haloethynyl)biphenyl derivatives of Fürstner et al. was carried out by DFT/M06 calculations to uncover the catalyst‐dependent selectivity of the reactions. The results revealed that the 6‐endo‐dig cyclization is the most favorable pathway in both InCl3‐ and AuCl‐catalyzed reactions. When AuCl is used, the 9‐bromophenanthrene product could be formed by consecutive 1,2‐H/1,2‐Br migrations from the Wheland‐type intermediate of the 6‐endo‐dig cyclization. However, in the InCl3‐catalyzed reactions, the chloride‐assisted intermolecular H‐migrations between two Wheland‐type intermediates are more favorable. These Cl‐assisted H‐migrations would eventually lead to 10‐bromophenanthrene through proto‐demetalation of the aryl indium intermediate with HCl. The cause of the poor selectivity of the PtCl2 catalyst in the experiments by the Fürstner group was predicted. It was found that both the PtCl2‐catalyzed alkyne–vinylidene rearrangement and the 5‐exo‐dig cyclization pathways have very close activation energies. Further calculations found the former pathway would lead eventually to both 9‐ and 10‐bromophenanthrene products, as a result of the Cl‐assisted H‐migrations after the cyclization of the Pt–vinylidene intermediate. Alternatively, the intermediate from the 5‐exo‐dig cyclization would be transformed into a relatively stable Pt–carbene intermediate irreversibly, which could give rise to the 9‐alkylidene fluorene product through a 1,2‐H shift with a 28.1 kcal mol?1 activation barrier. These findings shed new light on the complex product mixtures of the PtCl2‐catalyzed reaction. 相似文献
3.
Steglenko DV Kletsky ME Kurbatov SV Tatarov AV Minkin VI Goumont R Terrier F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(27):7592-7604
The Diels–Alder reaction of 4‐nitrobenzodifuroxan (NBDF) with 1‐methoxy‐3‐trimethylsilyloxy‐1,3‐butadiene has been investigated experimentally and theoretically. Treatment of NBDF with excess diene in chloroform at room temperature was found to afford a single product that contained a carbonyl functionality. Based on an X‐ray structure and NMR spectroscopic data, the product appeared to be a result of the hydrolysis of the OSiMe3 moiety of the thermodynamically more stable endo [2+4] cycloadduct, characterized by a cis arrangement of the MeO and NO2 functionalities. In situ NMR investigations of the interaction were carried out at room temperature in CDCl3 and at ?40 °C in deuterated acetonitrile. Calculations at the B3LYP/6‐31G* level in the gas phase and in acetonitrile were carried out under the assumption that the most stable cis conformation of the diene is also the most reactive in the interaction. The analysis revealed the NBDF/cis diene interaction involves the formation of a zwitterionic intermediate. Importantly, this intermediate is formed in two preferred conformations, which correspond to the endo and exo modes of approach of the reagents. Cyclization of these two identified conformations afforded the experimentally characterized endo and exo [2+4] cycloadducts. According to the calculations, the interconversion of the two conformers can either take place through a return to the pre‐reaction complexes or it can occur by rotation through an intermediate conformation of lesser stability. In view of the stepwise character of the interaction, the possibility that the intermediate zwitterion is the result of the interaction between NBDF and the trans diene could not be excluded. Calculations carried out with the most stable and more populated s‐trans conformer confirmed this idea and supported the role of the zwitterion in the overall interaction. 相似文献
4.
Zewang You Wei Song Sha Zhang Ouyue Jin Meiran Xie 《Journal of polymer science. Part A, Polymer chemistry》2013,51(22):4786-4798
exo‐Polynorbornenes containing bis(trifluoromethyl)biphenyl side groups were synthesized by ring‐opening metathesis polymerization using different Grubbs' catalysts, the microstructures of the polymer chains were established using NMR and IR spectroscopy. The influence of monomer and catalyst structures on chain microstructure was revealed and the correlation of properties with microstructure was investigated in detail. The exo‐poly(N‐3,5‐bis(trifluoromethyl)biphenyl‐norbornene‐pyrrolidine) (exo‐PTNP) and exo‐poly(N‐3,5‐bis(trifluoromethyl)biphenyl‐norbornene‐dicarboximide) (exo‐PTNDI) formed using Ru‐I show a trans double bond bias of 67% and 83%, respectively, whereas the corresponding polymers formed using Ru‐III have lower contents of trans double bond, 30% and 50%, respectively. Compared to the highly trans endo‐PTNP formed using Ru‐I , which is isotactic and has a dielectric constant of about 20, the endo‐PTNP formed using Ru‐III, the exo‐PTNDIs and the exo‐PTNPs formed using Ru‐I and Ru‐III all have different proportions of trans and cis double bonds, they are atactic and display relatively low dielectric constants, in the range 6 to 9. DSC measurements indicate some dependence of Tg, varying 161 to 221 °C, on tacticity and cis/trans ratios with higher trans contents tending towards higher Tg. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4786–4798 相似文献
5.
Cedric L. Hugelshofer Dr. Thomas Magauer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):15125-15136
We present a full account of the development of a strategy that culminated in the first total syntheses of the unique oxetane‐containing natural product (+)‐dictyoxetane and the macrocyclic diterpene (+)‐dolabellane V. Our retrosynthetic planning was guided by both classical and nonconventional strategies to construct the oxetane, which is embedded in an unprecedented 2,7‐dioxatricyclo[4.2.1.03,8]nonane ring system. Highlights of the successful approach include highly diastereoselective carbonyl addition reactions to assemble the full carbon skeleton, a Grob fragmentation to construct the 11‐membered macrocycle of (+)‐dolabellane V, and a bioinspired 4‐exo‐tet, 5‐exo‐trig cyclization sequence to form the complex dioxatricyclic framework of (+)‐dictyoxetane. Furthermore, an unprecedented strain‐releasing type I dyotropic rearrangement of an epoxide‐oxetane substrate was developed. 相似文献
6.
Miles A. Dunbar Shawna L. Balof Lawrence J. LaBeaud Bing Yu Dr. Andrew B. Lowe Dr. Edward J. Valente Dr. Hans‐Jörg Schanz Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12435-12446
The effect of the addition of H3PO4 on the ROMP activity of cyclooctene (COE) with first‐ [Cl2(PCy3)2Ru?CHPh] and second‐generation [(H2IMes)Cl2(PCy3)Ru?CHPh] Grubbs’ catalysts 1 and 4 (Cy=cyclohexyl, Ph=phenyl, Mes=2,4,6‐trimethylphenyl (mesityl)), their inhibited mixtures with 1‐methylimidazole (MIM), as well as their isolated bis‐N,N′‐dimethylaminopyridine (DMAP) derivatives [Cl2(PCy3)(DMAP)2Ru?CHPh)] ( 5 b ) and [Cl2(H2IMes)(DMAP)2Ru?CHPh] ( 7 b ) (DMAP=dimethylaminopyridine), a novel catalyst, has been investigated. The studies include the determination of their initiation rates, as well as a determination of the molecular weights and molecular weight distributions of the polymers obtained with these catalysts and catalyst mixtures from the exo‐7‐oxanorbornene derivative 11 . The structure of catalyst 7 b was confirmed by means of X‐ray diffraction. All N‐donor‐bearing catalysts or N‐donor‐containing catalyst mixtures not only exhibited elevated activity in the presence of acid, but also increased initiation rates. Using the reversible inhibition/activation protocol with MIM and H3PO4 enabled us to conduct controlled ROMP with catalyst 4 producing the isolated exo‐7‐oxanorbornene‐based polymer 12 with predetermined molecular weights and narrow molecular weight distributions. This effect was based on fast and efficient catalyst initiation in contrast to the parent catalyst 4 . Hexacoordinate complex 5 b also experienced a dramatic increase in initiation rates upon acid‐addition and the ROMP reactions became well‐controlled in contrast to the acid‐free reaction. In contrast, complex 7 b performs well‐controlled ROMP in the absence of acid, whereas the polymerization of the same monomer becomes less controlled in the presence of H3PO4. The closer evaluation of catalysts 5 b and 7 b demonstrated that their initiation rates exhibit a linear dependency on the substrate concentration in contrast to catalysts 1 and 4 . As a consequence, their initiation rates are determined by an associative step, not a dissociative step as seen for catalysts 1 and 4 . A feasible associative metathesis initiation mechanism is proposed. 相似文献
7.
Direct Carbocyclizations of Benzoic Acids: Catalyst‐Controlled Synthesis of Cyclic Ketones and the Development of Tandem aHH (acyl Heck–Heck) Reactions 下载免费PDF全文
Kelsey C. Miles Chi “Chip” Le Prof. Dr. James P. Stambuli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(36):11336-11339
The formation of exo‐methylene indanones and indenones from simple ortho‐allyl benzoic acid derivatives has been developed. Selective formation of the indanone or indenone products in these reactions is controlled by choice of ancillary ligand. This new process has a low environmental footprint as the products are formed in high yields using low catalyst loadings, while the only stoichiometric chemical waste generated from the reactants in the transformation is acetic acid. The conversion of the active cyclization catalyst into the Hermman–Beller palladacycle was exploited in a one‐pot tandem acyl Heck–Heck (aHH) reaction, and utilized in the synthesis of donepezil. 相似文献
8.
Friedrich Stierli Roland Prewo Jost H. Bieri Heinz Heimgartner 《Helvetica chimica acta》1983,66(5):1366-1375
Addition Reactions of 2-Amino-1-azetines with Cyclopropenones; Formation of Azepine Derivatives by Ring Expansion Reactions The reaction of 2-amino-1-azetines of type 6 with 2,3-diphenylcyclopropenone ( 1a ) in acetonitrile leads to azetol[1,2-α]pyrroles (cf. 7 and 9 , Schemes 3 and 4) in good yield. It is remarkable that in the reaction of 6a with 1a only endo- 7 is formed. With silicagel in ether endo- 7 isomerizes to the thermodynamically more stable exo- 7 (Schemes 3 and 6). The crystal structure of the latter compound has been established by X-ray crystallography. The reaction of 6a and 2-isopropyl-3-phenyl-cyclopropenone ( 1b ) yields only one product, which isomerizes with silicagel in ether to exo- 10 (Scheme 4). The structure of exo- 10 has been determined by NMR-spectroscopy. It seems reasonable that this structure results from a nucleophilic attack of the four-membered amidine to the phenyl-substituted C-atom of 1b. 相似文献
9.
Karen Lienkamp Christoph F. Kins Sterling F. Alfred Ahmad E. Madkour Gregory N. Tew 《Journal of polymer science. Part A, Polymer chemistry》2009,47(5):1266-1273
Unprotected exo,exo‐5‐norbornene‐2,3‐dicarboxylic acid and exo,exo‐7‐oxa‐5‐norbornene‐2,3‐dicarboxylic acid were polymerized via ring‐opening metathesis polymerization. This reaction yielded polymers with molecular weights (Mn from GPC) ranging from 31 to 242 kg/mol and polydispersity indices between 1.05 and 1.12, using Grubbs' third generation catalyst. The water solubility as a function of pH value of the polymers was investigated by dynamic light scattering (DLS). DLS and acid‐base titration revealed that the oxanorbornene polymer was water soluble over a wider pH range than its norbornene analog. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1266–1273, 2009 相似文献
10.
Prof. Duncan W. Bruce Prof. Yanan Gao Prof. José Nuno Canongia Lopes Dr. Karina Shimizu Dr. John M. Slattery 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(45):16113-16123
Liquid‐crystalline ionic liquids (LCILs) are ordered materials that have untapped potential to be used as reaction media for synthetic chemistry. This paper investigates the potential for the ordered structures of LCILs to influence the stereochemical outcome of the Diels–Alder reaction between cyclopentadiene and methyl acrylate. The ratio of endo‐ to exo‐product from this reaction was monitored for a range of ionic liquids (ILs) and LCILs. Comparison of the endo:exo ratios in these reactions as a function of cation, anion and liquid crystallinity of the reaction media, allowed for the effects of liquid crystallinity to be distinguished from anion effects or cation alkyl chain length effects. These data strongly suggest that the proportion of exo‐product increases as the reaction media is changed from an isotropic IL to a LCIL. A detailed molecular dynamics (MD) study suggests that this effect is related to different hydrogen bonding interactions between the reaction media and the exo‐ and endo‐transition states in solvents with layered, smectic ordering compared to those that are isotropic. 相似文献
11.
The Mechanism of NO Bond Cleavage in Rhodium‐Catalyzed CH Bond Functionalization of Quinoline N‐oxides with Alkynes: A Computational Study 下载免费PDF全文
Yingzi Li Song Liu Zisong Qi Xiaotian Qi Prof. Dr. Xingwei Li Prof. Dr. Yu Lan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(28):10131-10137
Metal‐catalyzed C?H activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N‐oxide is used as an arene source in C?H activation studies, the N?O bond can act as a directing group as well as an O‐atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline N?O bond and alkynes, which results in C?H activation and O‐atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a Rh?C bond, a reductive elimination to form an oxazinoquinolinium‐coordinated RhI intermediate, an oxidative addition to break the N?O bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop‐1‐yn‐1‐ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1‐phenyl‐2‐quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity‐determining step. These calculated data are consistent with the experimental observations. 相似文献
12.
Salomé Llabrés Dr. Esther Vicente‐García Dr. Sara Preciado Cristina Guiu Prof. Ramon Pouplana Prof. Rodolfo Lavilla Prof. F. Javier Luque 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13355-13361
The evolution of a ternary molecular system (imine, diene and nitrile) is analyzed to disclose the pathways leading to a divergent synthetic outcome. The Lewis acid catalyzed reaction between cyclohexadiene, 2‐phenyl‐indol‐3‐one and acetonitrile yields the imino‐Diels–Alder adduct as the major product together with minor amounts of the Mannich–Ritter‐amidine product. The experimental and computational data show that the relative orientation of the initial reactants dictates the synthetic outcome. The exo approach between imine and diene leads to the Diels–Alder adduct in a concerted process, whereas the endo mode leads to a polarized intermediate, which is trapped by acetonitrile to yield the multicomponent adduct. 相似文献
13.
Mitsuru Oka Kunihisa Baba Hitoshi Hamajima Ryoichi Unno Yukiharu Matsumoto Kensuke Nakamura Lulu Dong 《Journal of heterocyclic chemistry》2003,40(1):177-180
5‐Cyano‐1‐azabicyclo[3.3.0]octane ( 1 ) was prepared in one step from 1,7‐dichloro‐4‐heptanone ( 4 ) under mild conditions. The application of this method for the preparation of 5‐cyano‐4,6‐dimethyl‐1‐azabicy‐clo[3.3.0]octane ( 11 ) gave two diastereomers in equilibrium. The NMR measurements of 11 and its reduced compound 15 showed that the major isomer is the cis‐exo form, and the minor isomer is the trans form. Molecular orbital calculations indicated that the cis‐exo form is more stable than the trans form, in agreement with the experimental results. Furthermore, 6‐cyano‐1‐azabicyclo[4.3.0]nonane ( 17 ) and 1‐azabicy‐clo[4.4.0]decane ( 19 ), both including a six‐membered ring, were prepared from appropriate haloketones by using this double cyclization method. 相似文献
14.
Mousumi Ghosh Jeffrey L. Conroy Christopher T. Seto 《Angewandte Chemie (International ed. in English)》1999,38(4):514-516
The base‐promoted hydrolysis of amide substrates that contain a thiol substituent in the position α to the amide carbonyl group is effectively catalyzed by 4‐heterocyclohexanones [Eq. (1)]. The proposed mechanism of the hydrolysis reaction mimics that employed by serine proteases, and involves equilibrium binding of the substrate to the catalyst, formation of an acyl‐catalyst intermediate, and deacylation of the intermediate to release the product and regenerate the catalyst. 相似文献
15.
Meiran Xie Liya Zhang Yang Liao Liang Ding Chi Zeng Zewang You 《Journal of polymer science. Part A, Polymer chemistry》2011,49(23):4955-4963
A novel polymeric hollow nanostructure was generated using micellar template method through a three‐step procedure. First, the block copolymers were synthesized via ring‐opening metathesis polymerization by sequentially adding monomers 7‐oxanorborn‐5‐ene‐exo‐exo‐2,3‐dicarboxylic acid dimethyl ester and the mixture of norbornene and 2,3‐bis(2‐bromoisobutyryloxymethyl)‐5‐norbornene in chloroform, and also atom transfer radical polymerization of 4‐(3‐butenyl)styrene was carried out by using the as‐obtained block copolymer poly(7‐oxanorborn‐5‐ene‐exo,exo‐2,3‐dicarboxylic acid dimethylester)‐block‐poly(norbornene‐co‐2,3‐bis(2‐bromoisobutyryloxymethyl)‐5‐norbornene as macroinitiator to afford a graft copolymer bearing poly(4‐(3‐butenyl)styrene) branch poly(7‐oxanorborn‐5‐ene‐exo,exo‐2,3‐dicarboxylic acid dimethylester)‐block‐poly(norbornene‐co‐2,3‐bis(2‐bromoisobutyryloxymethyl)‐5‐norbornene)‐graft‐poly(4‐(3‐butenyl)styrene). Second, the shell‐crosslinked micelles were prepared by ruthenium‐mediated ring‐closing metathesis of poly(4‐(3‐butenyl)styrene) branches in intramicelle formed from the copolymers self‐assembly spontaneously in toluene. Finally, the hollowed spherical nanoparticles were presented by removing the micellar copolymer backbone through the cleavage of the ester bonds away from the crosslinked network of branches. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
16.
Yoshio Ando Yoshihiko Maezawa Jun Shimura Kei Kitamura Takashi Matsumoto Keisuke Suzuki 《化学:亚洲杂志》2020,15(6):828-832
For exploring general routes to the pluramycin‐class of antibiotics, including congeners with epoxide‐bearing side chains, syntheses of kidamycinone and its epoxide (epoxykidamycinone) have been achieved. At the stage of the A‐ring cyclization with alkene‐bearing side chain, the desired 6‐endo product was obtained as a major compound, although the corresponding undesired 5‐exo product was also formed. 相似文献
17.
Jun Nishimura Takashi Funaki Noriaki Saito Seiichi Inokuma Yosuke Nakamura So Tajima Toshitada Yoshihara Seiji Tobita 《Helvetica chimica acta》2005,88(6):1226-1239
Intramolecular [2+2] photocycloaddition of a dimeric vinylpyridine 1 through a singlet‐excited species efficiently formed the corresponding syn‐ and anti‐pyridinophanes 2 and 3 . The syn‐isomers were elucidated spectroscopically and by X‐ray crystallography as exo,syn‐configured. The high selectivity under formation of exo,syn‐ 2 was thoroughly investigated. Consequently, an exo‐outstretching effect, which is observed around the periphery of a face‐to‐face‐oriented system between two aromatic nuclei as a transition state, on cyclobutane ring formation was discovered for the first time. 相似文献
18.
Metal‐Free Radical 5‐exo‐dig Cyclizations of Phenol‐Linked 1,6‐Enynes for the Synthesis of Carbonylated Benzofurans 下载免费PDF全文
Ming Hu Dr. Ren‐Jie Song Prof. Dr. Jin‐Heng Li 《Angewandte Chemie (International ed. in English)》2015,54(2):608-612
A new metal‐free radical 5‐exo‐dig cyclization of phenol‐linked 1,6‐enynes with O2, 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), and tBuONO is described. With this general method, carbonylated benzofurans can be accessed through incorporation of two oxygen atoms into the product from O2 and TEMPO through dioxygen activation and oxidative cleavage of the N? O bond, respectively. 相似文献
19.
Dr. Yuan-He Li Dr. Su-Lei Zhang Dr. Yong Lu Bo Xiao Dr. Tian-Yu Sun Qian-Qian Xu Prof. Dr. Jia-Hua Chen Prof. Dr. Zhen Yang 《Angewandte Chemie (International ed. in English)》2023,62(33):e202303075
A highly enantioselective catalytic system for exo-Diels–Alder reactions was developed based on the newly discovered bispyrrolidine diboronates (BPDB). Activated by various Lewis or Brønsted acids, BPDB can catalyze highly stereoselective asymmetric exo-Diels–Alder reactions of monocarbonyl-based dienophiles. When 1,2-dicarbonyl-based dienophiles are used, the catalyst can sterically distinguish between the two binding sites, which leads to highly regioselective asymmetric Diels–Alder reactions. BPDB can be prepared as crystalline solids on a large scale and are stable under ambient condition. Single-crystal X-ray analysis of the structure for acid-activated BPDB indicated that its activation involves cleavage of a labile B←N bond. 相似文献
20.
In general, Lewis acid catalysts are metal‐based compounds that owe their reactivity to a low‐lying empty orbital. However, one potential Lewis acid that has received negligible attention as a catalyst is the carbocation. We have demonstrated the potential of the carbocation as a highly powerful Lewis acid catalyst for organic reactions. The stable and easily available triphenylmethyl (trityl) cation was found to be a highly efficient catalyst for the Diels–Alder reaction for a range of substrates. Catalyst loadings as low as 500 ppm, excellent yields, and good endo/exo selectivities were achieved. Furthermore, by changing the electronic properties of the substituents on the tritylium ion, the Lewis acidity of the catalyst could be tuned to control the outcome of the reaction. The ability of this carbocation as a Lewis acid catalyst was also further extended to the Michael reaction. 相似文献