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1.
Akio Urushima Daisuke Taura Makoto Tanaka Naomichi Horimoto Junki Tanabe Naoki Ousaka Tadashi Mori Eiji Yashima 《Angewandte Chemie (International ed. in English)》2020,59(19):7478-7486
A novel 2,6‐anthrylene‐linked bis(m‐terphenylcarboxylic acid) strand ( 1 ) self‐associates into a racemic double‐helix. In the presence of chiral mono‐ and diamines, either a right‐ or left‐handed double‐helix was predominantly induced by chiral amines sandwiched between the carboxylic acid strands with accompanying stacking of the two prochiral anthracene linker units in an enantiotopic face‐selective way, as revealed by circular dichroism and NMR spectral analyses. The photoirradiation of the optically active double helices complexed with chiral amines proceeded in a diastereo‐ (anti or syn) and enantiodifferentiating way to afford the chiral anti‐photodimer with up to 98 % enantiomeric excess when (R)‐phenylethylamine was used as a chiral double‐helix inducer. The resulting optically active anti‐photodimer can recognize the chirality of amines and diastereoselectively complex with chiral amines. 相似文献
2.
The title compounds were prepared by aldol reaction of anisaldehyde and the respective N,N‐dibenzyl glycinates. Deprotection of the nitrogen atom with Pearlman’s catalyst delivered the unprotected β‐hydroxytyrosine esters, which were further N‐protected as N,N‐phthaloyl (Phth) and N‐fluorenylmethylcarbonyloxy (Fmoc) derivatives. The Friedel–Crafts reaction with various arenes was studied employing these alcohols as electrophiles. It turned out that the facial diastereoselectivitiy depends on the nitrogen protecting group and on the ester group. The unprotected substrates (NH2) gave preferentially syn‐products but the anti‐selectivity increased when going from NHFmoc over NPhth to NBn2. If the ester substituent was varied the syn‐preference increased in the order Me <Et <iPr. The reactions were shown to be fully stereoconvergent and proceeded under kinetic product control. A model is suggested to explain the facial diastereoselectivity based on a conformationally locked benzylic cation intermediate. The reactions are preparatively useful for the N‐unprotected isopropyl ester, which gave Friedel–Crafts alkylation products with good syn‐selectivity (anti/syn=21:79 to 7:93), and for the N,N‐dibenzyl‐protected methyl ester, which led preferentially to anti‐products (anti/syn=80:20 to >95:5). Upon acetylation of the latter compound to the respective acetate, Bi(OTf)3‐catalyzed alkylation reactions became possible, in which silyl enol ethers served as nucleophiles. The respective alkylation products were obtained in high yield and with excellent anti‐selectivitiy (anti/syn≥95:5). 相似文献
3.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(41):12808-12812
Higher‐order super‐helical structures derived from biological molecules are known to evolve through opposite coiling of the initial helical fibers, as seen in collagen protein. A similar phenomenon is observed in a π‐system self‐assembly of chiral oligo(phenyleneethylene) derivatives (S )‐ 1 and (R )‐ 1 that explains the unequal formation of both left‐ and right‐handed helices from molecule having a specific chiral center. Concentration‐ and temperature‐dependent circular dichroism (CD) and UV/Vis spectroscopic studies revealed that the initial formation of helical aggregates is in accordance with the molecular chirality. At the next level of hierarchical self‐assembly, coiling of the fibers occurs with opposite handedness, thereby superseding the command of the molecular chirality. This was confirmed by solvent‐dependent decoiling of super‐helical structures and concentration‐dependent morphological analysis. 相似文献
4.
Ottorino DeLucchi Arif Datan Aliye Altunda Fabrizio Fabris Metin Balci 《Helvetica chimica acta》2004,87(9):2364-2367
An efficient synthetic route to the concave‐shaped, potentially ionophoric syn‐ and anti‐isomers of 5,6,11,12,17,18‐hexahydro‐5,18:6,11:12,17‐triepoxytrinaphthylene ( 4 ) was elaborated. Starting from ‘oxabenzonorbornadiene’ ( 5 ), the stannylated precursor 9 was prepared in three steps, followed by cyclotrimerization catalyzed by copper(I) thiophene‐2‐carboxylate (CuTC) , which afforded 4 in a syn/anti ratio of 5 : 4. 相似文献
5.
A Concise and Highly Enantioselective Total Synthesis of (+)‐anti‐ and (−)‐syn‐Mefloquine Hydrochloride: Definitive Absolute Stereochemical Assignment of the Mefloquines 下载免费PDF全文
Ettore J. Rastelli Prof. Don M. Coltart 《Angewandte Chemie (International ed. in English)》2015,54(47):14070-14074
A concise asymmetric (>99:1 e.r.) total synthesis of (+)‐anti‐ and (?)‐syn‐mefloquine hydrochloride from a common intermediate is described. The key asymmetric transformation is a Sharpless dihydroxylation of an olefin that is accessed in three steps from commercially available materials. The Sharpless‐derived diol is converted into either a trans or cis epoxide, and these are subsequently converted into (+)‐anti‐ and (?)‐syn‐mefloquine, respectively. The synthetic (+)‐anti‐ and (?)‐syn‐mefloquine samples were derivatized with (S)‐(+)‐mandelic acid tert‐butyldimethylsilyl ether, and a crystal structure of each derivative was obtained. These are the first X‐ray structures for mefloquine derivatives that were obtained by coupling to a known chiral, nonracemic compound, and provide definitive confirmation of the absolute stereochemistry of (+)‐anti‐ as well as (?)‐syn‐mefloquine. 相似文献
6.
An expedient concise total synthesis of (+)‐7‐epigoniodiol, (?)‐8‐epigoniodiol, and (+)‐9‐deoxygoniopypyrone is accomplished. The key transformations include a catalytic hydroxylation and base‐mediated N‐(acetyl)oxazolidinone addition reactions, which could set the consecutive OH motif that is either syn,syn or syn,anti with high diastereoselectivity. Moreover, this approach envisioned to facilitate the synthesis of other representatives of the family with structural and stereochemical variation. 相似文献
7.
Binuclear trans‐Bis(β‐iminoaryloxy)palladium(II) Complexes Doubly Linked with Pentamethylene Spacers: Structure‐Dependent Flapping Motion and Heterochiral Association Behavior of the Clothespin‐Shaped Molecules 下载免费PDF全文
Masaya Naito Hiroyuki Souda Hiroshi Koori Dr. Naruyoshi Komiya Prof. Takeshi Naota 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(23):6991-7000
The synthesis, structure, and solution‐state behavior of clothespin‐shaped binuclear trans‐bis(β‐iminoaryloxy)palladium(II) complexes doubly linked with pentamethylene spacers are described. Achiral syn and racemic anti isomers of complexes 1 – 3 were prepared by treating Pd(OAc)2 with the corresponding N,N′‐bis(β‐hydroxyarylmethylene)‐1,5‐pentanediamine and then subjecting the mixture to chromatographic separation. Optically pure (100 % ee) complexes, (+)‐anti‐ 1 , (+)‐anti‐ 2 , and (+)‐anti‐ 3 , were obtained from the racemic mixture by employing a preparative HPLC system with a chiral column. The trans coordination and clothespin‐shaped structures with syn and anti conformations of these complexes have been unequivocally established by X‐ray diffraction studies. 1H NMR analysis showed that (±)‐anti‐ 1 , (±)‐anti‐ 2 , syn‐ 2 , and (±)‐anti‐ 3 display a flapping motion by consecutive stacking association/dissociation between cofacial coordination planes in [D8]toluene, whereas syn‐ 1 and syn‐ 3 are static under the same conditions. The activation parameters for the flapping motion (ΔH≠ and ΔS≠) were determined from variable‐temperature NMR analyses as 50.4 kJ mol?1 and 60.1 J mol?1 K?1 for (±)‐anti‐ 1 , 31.0 kJ mol?1 and ?22.7 J mol?1 K?1 for (±)‐anti‐ 2 , 29.6 kJ mol?1 and ?57.7 J mol?1 K?1 for syn‐ 2 , and 35.0 kJ mol?1 and 0.5 J mol?1 K?1 for (±)‐anti‐ 3 , respectively. The molecular structure and kinetic parameters demonstrate that all of the anti complexes flap with a twisting motion in [D8]toluene, although (±)‐anti‐ 1 bearing dilated Z‐shaped blades moves more dynamically than I‐shaped (±)‐anti‐ 2 or the smaller (±)‐anti‐ 3 . Highly symmetrical syn‐ 2 displays a much more static flapping motion, that is, in a see‐saw‐like manner. In CDCl3, (±)‐anti‐ 1 exhibits an extraordinary upfield shift of the 1H NMR signals with increasing concentration, whereas solutions of (+)‐anti‐ 1 and the other syn/anti analogues 2 and 3 exhibit negligible or slight changes in the chemical shifts under the same conditions, which indicates that anti‐ 1 undergoes a specific heterochiral association in the solution state. Equilibrium constants for the dimerizations of (±)‐ and (+)‐anti‐ 1 in CDCl3 at 293 K were estimated by curve‐fitting analysis of the 1H NMR chemical shift dependences on concentration as 26 M ?1 [KD(racemic)] and 3.2 M ?1 [KD(homo)], respectively. The heterochiral association constant [KD(hetero)] was estimated as 98 M ?1, based on the relationship KD(racemic)=1/2 KD(homo)+1/4 KD(hetero). An inward stacking motif of interpenetrative dimer association is postulated as the mechanistic rationale for this rare case of heterochiral association. 相似文献
8.
The silver(I)‐catalyzed synthesis picture of axially chiral allenes based on propargylamines has been outlined using density functional theory (DFT) method for the first time. Our calculations find that, the coordination of silver(I) into triple bond of propargylamines at anti‐position of nitrogen shows a stronger activation on the triple bond than that at cis‐position, which is favorable for the subsequent hydrogen transfer. The NBO charge analysis for the hydrogen transfer affirms the experimental speculation that this step is a hydride transfer process. The energy barrier of the anti‐periplanar elimination of vinyl‐silver is 26.9 kJ·mol?1 lower than that of the syn‐periplanar elimination, supporting that (?)‐allene is the main product of this reaction. In a word, the most possible route for this reaction is that the silver(I) coordinates into the triple bond of propargylamines at anti‐position of nitrogen, then the formed silver(I) complex undergoes a hydride transfer to give a vinyl‐silver, finally the vinyl‐silver goes through an anti‐periplanar elimination to give (?)‐allene. The hydride transfer with the energy barrier of 44.8 kJ·mol?1 is the rate‐limiting step in whole catalytic process. This work provides insight into why this reaction has a very high enantioselectivity. 相似文献
9.
Lívia O. A. Ferreira Ana Karoline S. M. Valdo Jos Antnio Nascimento Neto Leandro Ribeiro Jefferson R. D. da Silva Luiz H. K. Queiroz Caridad N. Perez Felipe T. Martins 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):694-701
We report a new polymorph of (1E,4E)‐1,5‐bis(4‐fluorophenyl)penta‐1,4‐dien‐3‐one, C17H12F2O. Contrary to the precedent literature polymorph with Z′ = 3, our polymorph has one half molecule in the asymmetric unit disordered over two 50% occupancy sites. Each site corresponds to one conformation around the single bond vicinal to the carbonyl group (so‐called anti or syn). The other half of the bischalcone is generated by twofold rotation symmetry, giving rise to two half‐occupied and overlapping molecules presenting both anti and syn conformations in their open chain. Such a disorder allows for distinct patterns of intermolecular C—H…O contacts involving the carbonyl and anti‐oriented β‐C—H groups, which is reflected in three 13C NMR chemical shifts for the carbonyl C atom. Here, we have also assessed the cytotoxicity of three symmetric bischalcones through their in vitro antitumour potential against three cancer cell lines. Cytotoxicity assays revealed that this biological property increases as halogen electronegativity increases. 相似文献
10.
β,β‐(1,4‐Dithiino)subporphyrin Dimers Capturing Fullerenes with Large Association Constants 下载免费PDF全文
Kota Yoshida Prof. Dr. Atsuhiro Osuka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9396-9403
β,β‐(1,4‐Dithiino)subporphyrin dimers 7‐syn and 7‐anti were synthesized by the nucleophilic aromatic substitution reaction of 2‐bromo‐3‐(4‐methoxyphenylsulfonyl)subporphyrin 4 with 2,3‐dimercaptosubporphyrin 5 under basic conditions followed by axial arylation. Additions of C60 or C70 to a dilute solution of 7‐anti (ca. 10?6 m ) in toluene did not cause appreciable UV/Vis spectral changes, while similar additions to a concentrated solution (ca. 10?3 m ) resulted in precipitation of complexes. In contrast, dimer 7‐syn captured C60 and C70 in different complexation stoichiometries in toluene; a 1:1 manner and a 2:1 manner, respectively, with large association constants; Ka=(1.9±0.2)×106 m ?1 for C60@ 7‐syn , and K1=(1.6±0.5)×106 and K2=(1.8±0.9)×105 m ?1 for C70@( 7‐syn )2. These association constants are the largest for fullerenes‐capture by bowl‐shaped molecules reported so far. The structures of C60@ 7‐anti , C70@ 7‐anti , C60@ 7‐syn , and C70@ 7‐syn have been determined by single‐crystal X‐ray diffraction analysis. 相似文献
11.
Asymmetric anti‐Selective Michael Reaction of Imidazole‐Modified Ketones with trans‐β‐Nitroalkenes 下载免费PDF全文
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
12.
Prof. Dr. Yolanda Arroyo Prof. Dr. M. Ascensión Sanz‐Tejedor Dr. Alejandro Parra Prof. Dr. José Luis García Ruano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5314-5318
Asymmetric nucleophilic monofluoroalkylation of a broad range of aldehydes with an α‐fluoro‐γ‐sulfinylbenzyl carbanion takes place with complete control of the facial selectivity at the carbanion and good to high anti‐diastereoselectivity to give easily separable mixtures of two optically pure 1,2‐fluorohydrin derivatives (up to 24:1 anti/syn). Separation and removal of the p‐tolylsulfinyl group with tBuLi provides enantiomerically pure anti‐1,2‐disubstituted‐1,2‐fluorohydrins, whereas α‐fluorobenzylketones can be obtained by desulfinylation of the mixture followed by pyridinium chlorochromate oxidation (one‐pot process). 相似文献
13.
Hartmut Fuess Michaela Schwarz Erich F. Paulus Jens Hartung Ingrid Svoboda 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(7):o386-o388
The title compound, C20H18ClNOS2, is a thiazole‐derived thiohydroxamic acid O‐ester. The value of Z′ is 3 and the asymmetric unit comprises three molecules of identical helicity along the N—O bond. Two of these show an anti and the third a syn arrangement of substituents attached in positions 3 and 4 to the 1,3‐thiazole nucleus. 相似文献
14.
Amalija Golobi
Martina Malekovi
Primo egedin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(3):m102-m104
The novel title polymeric copper(II) complex, {Na2[Cu3‐(CHO2)8]}n, consists of sodium cations and infinite anionic chains, in which neutral dinuclear [Cu2(O2CH)4] moieties alternate with dianionic [Cu(O2CH)4]2− units. Both metal‐containing moieties are located on crystallographic inversion centers. The syn–syn bridging configuration between the mononuclear and dinuclear components yields a structure that is significantly more dense than the structures previously reported for mononuclear–dinuclear copper(II) carboxylates with syn–anti or anti–anti bridging modes. 相似文献
15.
The influence of valine side chains on the folding/unfolding equilibrium and, in particular, on the 314‐helical propensity of β3‐peptides were investigated by means of molecular‐dynamics (MD) simulation. To that end, the valine side chains in two different β3‐peptides were substituted by leucine side chains. The resulting four peptides, of which three have never been synthesized, were simulated for 150 to 200 ns at 298 and 340 K, starting from a fully extended conformation. The simulation trajectories obtained were compared with respect to structural preferences and folding behavior. All four peptides showed a similar folding behavior and were found to predominantly adopt 314‐helical conformations, irrespective of the presence of valine side chains. No other well‐defined conformation was observed at significant population in any of the simulations. Our results imply that β3‐peptides show a structural preference for 314‐helices independent of the branching nature of the side chains, in contrast to what has been previously proposed on the basis of circular‐dichroism (CD) measurements. 相似文献
16.
Sari M. Kunnari Raija Oilunkaniemi Risto S. Laitinen Markku Ahlgren 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):o610-o611
The novel title tetraselenacalix[4]arene, C16H8S4Se4 or [(C4H2S)Se]4, has a centrosymmetric cyclic molecular structure with approximate C2h molecular symmetry. The four thienyl rings are joined together by Se bridges and exhibit a syn–syn–anti–anti arrangement around the molecule. The lattice consists of skewed stacks of molecules, with chalcogen–chalcogen close contacts binding the stacks together, forming a two‐dimensional network of molecules. 相似文献
17.
Jean-Claude Daran Nicolas Gimeno Maryse Gouygou Jrme Volkman 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(5):523-528
The self‐assembly of ditopic bis(1H‐imidazol‐1‐yl)benzene ligands ( L H) and the complex (2,2′‐bipyridyl‐κ2N,N′)bis(nitrato‐κO)palladium(II) affords the supramolecular coordination complex tris[μ‐bis(1H‐imidazol‐1‐yl)benzene‐κ2N3:N3′]‐triangulo‐tris[(2,2′‐bipyridyl‐κ2N,N′)palladium(II)] hexakis(hexafluoridophosphate) acetonitrile heptasolvate, [Pd3(C10H8N2)3(C12H10N4)3](PF6)6·7CH3CN, 2 . The structure of 2 was characterized in acetonitrile‐d3 by 1H/13C NMR spectroscopy and a DOSY experiment. The trimeric nature of supramolecular coordination complex 2 in solution was ascertained by cold spray ionization mass spectrometry (CSI–MS) and confirmed in the solid state by X‐ray structure analysis. The asymmetric unit of 2 comprises the trimetallic Pd complex, six PF6? counter‐ions and seven acetonitrile solvent molecules. Moreover, there is one cavity within the unit cell which could contain diethyl ether solvent molecules, as suggested by the crystallization process. The packing is stabilized by weak inter‐ and intramolecular C—H…N and C—H…F interactions. Interestingly, the crystal structure displays two distinct conformations for the L H ligand (i.e. syn and anti), with an all‐syn‐[Pd] coordination mode. This result is in contrast to the solution behaviour, where multiple structures with syn/anti‐ L H and syn/anti‐[Pd] are a priori possible and expected to be in rapid equilibrium. 相似文献
18.
Flash‐vacuum pyrolysis of the quadricyclane derivative 5a at 350° afforded the oxabishomocubane 9a , whose structure was confirmed by an INADEQUATE‐NMR experiment. A computational investigation of the mechanism of this unexpected reaction by DFT and CASPT2‐SCF methods indicated that the reaction path of lowest energy involves a quadricyclane/oxaquadricyclane ( 5 / 12 ) isomerization, followed by a well‐established cycloreversion of 12 to the carbonyl ylide 16 , which subsequently undergoes an intramolecular 1,3‐dipolar cycloadditon to 9 . The lowest‐energy path of the thermal isomerization of the syn‐quadricyclane 6c is its conversion to the syn ‐ sesquinorbornatriene 8c . The corresponding anti‐isomer 5c , however, shows the capability of a degenerate quadricyclane/quadricyclane rearrangement. 相似文献
19.
Masaki Shimizu Prof. Dr. Katsuhiro Shimono Dr. Tamejiro Hiyama Prof. Dr. 《化学:亚洲杂志》2007,2(9):1142-1149
Treatment of (Z)‐1,2,3,4‐tetrakis(pinacolatoboryl)but‐2‐ene, prepared from 2,3‐bis(pinacolatoboryl)buta‐1,3‐diene and bis(pinacolato)diboron, with three molar equivalents of aldehyde in toluene at 100 °C gave the 2,3‐bis(alkylidene)alkane‐1,5‐anti‐diol as a single stereoisomer. The reaction is applicable to both aromatic and α‐unbranched aliphatic aldehydes. The 1,5‐anti‐diols were also synthesized by the one‐pot preparation/triple‐aldehyde addition of the tetraborylated butene. Experimental results for the stepwise treatment of the butene with two types of aldehydes suggest that the rate‐determining step of the triple‐aldehyde addition is the third allylation. 相似文献
20.
The aldol reactions of 2‐arylimino‐3‐aryl‐thiazolidine‐4‐ones with benzaldehyde carried out at ?78 °C were found to produce sec‐carbinols. Intramolecular hydrogen bonding within the aldol products forming a six‐membered ring enabled the assignment of stereochemistries of the major and minor diastereomers via analysis of the syn and anti 3JH,H 1H NMR coupling constants. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献