共查询到20条相似文献,搜索用时 875 毫秒
1.
Dr. Simona Rizzo Prof. Tiziana Benincori Dr. Valentina Bonometti Dr. Roberto Cirilli Prof. Patrizia R. Mussini Prof. Marco Pierini Dr. Tullio Pilati Prof. Francesco Sannicolò 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):182-194
A series of tris‐aryl phosphanes, structurally designed to exist as residual enantiomers or diastereoisomers, bearing substituents differing in size and electronic properties on the aryl rings, were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation potential determined by voltammetry. The configurational stability of residual phosphanes, evaluated by dynamic HPLC on a chiral stationary phase or/and by dynamic 1H and 31P NMR spectroscopy, was found to be rather modest (barriers of about 18–20 kcal mol?1), much lower than that shown by the corresponding phosphane oxides (barriers of about 25–29 kcal mol?1). For the first time, the residual antipodes of a tris‐aryl phosphane were isolated in enantiopure state and the absolute configuration assigned to them by single‐crystal anomalous X‐ray diffraction analysis. In this case, the racemization barrier could be calculated also by CD signal decay kinetics. A detailed computational investigation was carried out to clarify the helix reversal mechanism. Calculations indicated that the low configurational stability of tris‐aryl phosphanes can be attributed to an unexpectedly easy phosphorus pyramidal inversion which, depending upon the substituents present on the blades, can occur even on the most stable of the four conformers constituting a single residual stereoisomer. 相似文献
2.
Tiziana Benincori Prof. Andrea Marchesi Dr. Tullio Pilati Dr. Alessandro Ponti Dr. Simona Rizzo Dr. Francesco Sannicolò Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(1):94-105
Residual stereoisomerism is a form of stereoisomerism scarcely considered so far for applicative purposes, though extremely interesting, since the production of stereoisomers does not involve classical rigid stereogenic elements. In three‐bladed propeller‐shaped molecules, a preferred stereomerization mechanism, related to the correlated rotation of the rings, allows the free interconversion of stereoisomers inside separated sets (the residual stereoisomers) that can interconvert through higher energy pathways. In light of possible future applications as chiral ligands for transition metals in stereoselective processes, some C3‐symmetric phosphorus‐centered propellers, which could exist as residual enantiomers, are synthesized and the possibility of resolving their racemates into residual antipodes is explored. While the tris(aryl)methanes are configurationally stable at room temperature, only selected tris(aryl)phosphane oxides display a configurational stability high enough to allow resolution by HPLC on a chiral stationary phase (CSP HPLC) at a semipreparative level at room temperature. Stability was evaluated through different techniques (circular dichroism (CD) signal decay, dynamic CSP HPLC (CSP DHPLC), dynamic NMR analysis (DNMR)) and the results compared and discussed. Phosphanes were found much less stable than the corresponding phosphane oxides, for which preliminary calculations suggest that the three‐ring‐flip enantiomerization mechanism (M0) would be easier than phosphorus pyramidal inversion. The parameters affecting the configurational stability of the residual enantiomers of C3‐symmetric propellers are discussed. 相似文献
3.
Prof. Tiziana Benincori Dr. Valentina Bonometti Dr. Roberto Cirilli Prof. Patrizia R. Mussini Dr. Andrea Marchesi Prof. Marco Pierini Dr. Tullio Pilati Dr. Simona Rizzo Prof. Francesco Sannicolò 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):165-181
A series of tris‐aryl phosphane oxides existing as residual enantiomers or diastereoisomers with substituents on the aryl rings differing in size and electronic properties were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation and reduction potentials together with those of the corresponding “blade bromides” (i.e., the naphthalene derivatives displaying the same substitution pattern of the tris‐naphthyl phosphane oxide blades, with a bromo substituent where the phosphorus atom is located) determined by CV. The residual stereoisomeric phosphane oxides were isolated in a stereochemically pure state and were found to be highly configurationally stable at room temperature (stereoisomerization barriers of about 27 kcal mol?1). The chiroptical properties of the residual stereoisomers and the assignments of absolute configuration are discussed. The configurational stability of residual tris‐aryl phosphane oxides was found to be scarcely influenced by the electronic properties of the substituents present on the aromatic rings constituting the blades, while steric effects play the most relevant role. Detailed theoretical calculations are in agreement with the experimental results and also contribute to a rational interpretation of the stereodynamics of these systems. 相似文献
4.
Attila C. Bényei Yoshiki Ozawa Koshiro Toriumi József Bakos 《Journal of organometallic chemistry》2007,692(9):1845-1851
The structure of tris(2,4-xylyl)phosphane (1) is reported and supramolecular assembly of gua+ salt of tris(2,4-dimethyl-5-sulfonatophenyl)phosphane co-crystal with guanidine chloride (2) is analyzed in detail. Weaving hydrogen bond ribbons with polar and apolar stabilizing pillars as well as stacking interaction of phenyl rings resulting sixfold phenyl embraces interpenetrating with the polar networks were found. Both compounds are racemate, show propeller chirality and 2 crystallizes in non-centrosymmetric space group (C3 symmetry) with the ortho-methyl groups outside of the molecular cone. According to the DFT calculations on the anion of 2, the high barrier of concerted ring rotation opens the possibility of resolving the enantiomers through hydrogen bonds to chiral donors. 相似文献
5.
《Analytical letters》2012,45(6):1245-1254
ABSTRACT Racemic 4-aryl-1,2,3,4,5,6,7,8-octahydroquinazoline-2-thiones were resolved into their enantiomers by HPLC on cellulose tris(4-methylbenzoate) coated on silica gel using ethanol:n-hexane (70:30) as a mobile phase. A convenient method for preparation of cellulose tris(4-methylbenzoate) chiral stationary phase was described and the enantiomers were characterized by some chromatographic data. 相似文献
6.
Ekaterina V. Bakhmutova Heinrich Nth Rosalinda Contreras Bernd Wrackmeyer 《无机化学与普通化学杂志》2001,627(8):1846-1854
Pseudo‐ephedrine derived 2‐imino‐1,3‐thiazolidine 1 reacts with tris(diethylamino)phosphane by stepwise replacement of the diethylamino group to give the mono‐, bis‐ and tris(imino)phosphanes 2 , 3 and 4 , respectively, of which 4 could be isolated in pure state. The analogous reaction with diethylamino‐diphenylphosphane affords the imino‐diphenylphosphane 5 . The iminophosphanes react with sulfur or selenium to give the corresponding phosphorus(V) compounds. In contrast, the reaction of the iminophosphanes with oxygen is very slow; anhydrous trimethylamine N‐oxide reacts in the melt with the phosphanes to give the oxides 4(O) and 5(O) . The molecular structures of 4(O) (in mixture with 4 ), 4(Se) , 5(S) and 5(Se) were determined by X‐ray analysis. In all cases the ring‐sulfur and the phosphorus atoms are in cis‐positions at the C=N bonds. The analogous solution structures were determined by 1H, 13C, 15N, 31P and 77Se NMR spectroscopy. In the case of the compounds 5 , 5(O) , 5(S) and 5(Se) the isotope‐induced chemical shifts 1δ14/15N(31P) were determined, using INEPT‐HEED experiments. 相似文献
7.
A Quintuple [6]Helicene with a Corannulene Core as a C5‐Symmetric Propeller‐Shaped π‐System 下载免费PDF全文
Kenta Kato Prof. Dr. Yasutomo Segawa Prof. Dr. Lawrence T. Scott Prof. Dr. Kenichiro Itami 《Angewandte Chemie (International ed. in English)》2018,57(5):1337-1341
The synthesis and structural analysis of a quintuple [6]helicene with a corannulene core is reported. The compound was synthesized from corannulene in three steps including a five‐fold intramolecular direct arylation. X‐ray crystallographic analysis revealed a C5‐symmetric propeller‐shaped structure and one‐dimensional alignment in the solid state. The enantiomers of the quintuple [6]helicene were successfully separated by HPLC, and the chirality of the two fractions was identified by CD spectroscopy. A kinetic study yielded a racemization barrier of 34.2 kcal mol?1, which is slightly lower than that of pristine [6]helicene. DFT calculations indicate a rapid bowl‐to‐bowl inversion of the corannulene moiety and a step‐by‐step chiral inversion pathway for the five [6]helicene moieties. 相似文献
8.
Dirk Wesenberg Corinna Bleuel Gerd‐Joachim Krauss Martin G. Schmid Michael Weiss Gerald Gübitz 《Biomedical chromatography : BMC》2010,24(10):1125-1129
The development of methods for the separation of the enantiomers of fenoterol by chiral HPLC and capillary zone electrophoresis (CZE) is described. For the HPLC separation precolumn fluorescence derivatization with naphthyl isocyanate was applied. The resulting urea derivatives were resolved on a cellulose tris(3,5‐dimethylphenylcarbamate)‐coated silica gel column employing a column switching procedure. Detection was carried out fluorimetrically with a detection limit in the low ng/mL range. The method was adapted to the determination of fenoterol enantiomers in rat heart perfusates using liquid–liquid extraction. As an alternative a CE method was used for the direct separation of fenoterol enantiomers comparing different cyclodextrin derivatives as chiral selectors. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
9.
Lukas Hintermann Dr. Tuan Thanh Dang Dr. Aurélie Labonne Dr. Thomas Kribber Dipl.‐Gyml. Li Xiao Dr. Pance Naumov Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(29):7167-7179
The family of AZARYPHOS (aza–aryl–phosphane) phosphane ligands, containing a phosphine unit and sterically shielded nitrogen lone pairs in the ligand periphery, is introduced as a tool for developing ambifunctional catalysis by the metal center and nitrogen lone pairs in the ligand sphere. General synthetic strategies have been developed to synthesize over 25 examples of structurally diverse (6‐aryl‐2‐pyridyl)phosphanes (ARPYPHOS), (6‐alkyl‐2‐pyridyl)phosphanes (ALPYPHOS), 4,6‐disubsituted 1,3‐diazin‐2‐ylphosphanes or 1,3,5‐triazin‐2‐ylphosphanes, quinazolinylphosphanes, quinolinylphosphanes, and others. The scalable syntheses proceed in a few steps. The incorporation of AZARYPHOS ligands ( L ) into complexes [RuCp( L )2(MeCN)][PF6] (Cp=cyclopentadienyl) gives catalysts for the anti‐Markovnikov hydration of terminal alkynes of the highest known activities. Electronic and steric ligand effects modulate the reaction kinetics over a range of two orders of magnitude. These results highlight the importance of using structurally diverse ligand families in the process of developing cooperative ambifunctional catalysis by a metal and its ligand. 相似文献
10.
Guogang Liu Tobias Koch Yan Li Nikos L. Doltsinis Zhaohui Wang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(1):184-189
A novel kind of nanographene imide, namely pentaperylene decaimides (PPD) featuring dual‐core sixfold [5]helicenes and ten imide groups, was efficiently obtained. Among the possible 28 stereoisomers, which include 14 pairs of enantiomers, only one pair of enantiomers was obtained selectively which could be separated by chiral HPLC. Single‐crystal X‐ray diffraction analyses revealed that it exhibits a D2‐symmetric “four‐bladed propeller” conformation composed of conjoined double “three‐bladed propeller”, which is very stable and could not convert into other conformations even when heated up to 200 °C. Meanwhile, enantiomerically pure PPD also exhibits an excellent resistance to thermally induced racemization, which makes it a promising candidate for various applications in chiral material science. 相似文献
11.
A simple chiral high‐performance liquid chromatography (HPLC) method with ultraviolet (UV) detection was developed and validated for measuring Cloquintocet‐mexyl (ClM) enantiomers and clodinafop‐propargyl (CP) using cellulose tris‐(3,5‐dimethylphenylcarbamate) (CDMPC) as chiral stationary phase (CSP). The effects of mobile phase composition and column temperature on the ClM enantiomer separation were investigated. Good separation was achieved by using a mixture of n‐hexane and n‐propanol as mobile phase. Based on the chiral HPLC method, enantioselective quantitative determination analysis methods for this herbicide combined with CP in diluted plasma were developed and validated. The assay method was linear over a range of concentrations (0.5–100 µg/mL) in diluted plasma and the mean recovery was greater than 80% for both enantiomers and CP. The limits of quantification and detection for both ClM enantiomers and CP were 0.5 and 0.2 µg/mL, respectively. Intra‐ and interday relative standard deviations did not exceed 10% for three tested concentrations. The result suggested that the degradation of ClM enantiomers was stereoselective in rabbit plasma, and both rac‐ClM and CP degraded quickly in plasma, showing that the main existing forms with biological effect in animals are their metabolites. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
12.
Babett Krauss Clemens Mügge Adolf Zschunke Friedrich Krech Michaela Flock 《无机化学与普通化学杂志》2002,628(3):580-588
1‐Phosphabicyclo[2.2.1]heptanes Exo‐endo‐ and exo‐exo‐2.6‐dimethyl‐1‐phosphabicyclo [2.2.1]heptane have been obtained by cyclization of 2‐methyl‐4‐(2‐propenyl)phospholane in the presence of the complex base, sodium salt of diethylenglycolmonoethylether ‐ sodium amide in THF (NAMEDEG). The bicyclic phosphanes are characterized by reac‐tions with selenium, sulfur, (CH3)2SeO, CH3I and HSO3F, respectively, elemental analysis, X‐ray crystal structure analysis as well as 1H, 13C, 31P NMR spectral measurements. The steric demand of these phosphanes as complex ligands has been estimated from the P, H coupling constants of the phosphonium fluorosulphates according to the Tolman model. The phosphane selenides were found to display the lowest values for the 1J(Se, P) coupling constant, found up to now for alicyclic and cyclic aliphatic tertiary phosphane selenides. The nJ(P, H)‐ and nJ(H, H)n=2, 3 coupling constants have been extracted from the proton spectra at 600 MHz by computerized analysis. 相似文献
13.
Babett Krauss Clemens Mügge Burkhard Ziemer Adolf Zschunke Friedrich Krech 《无机化学与普通化学杂志》2001,627(7):1542-1552
1‐Phosphabicyclo[3.2.1]octanes 1‐Phosphabicyclo[3.2.1]octane has been obtained by free‐radical cyclization of (2‐vinyl‐4‐pentenyl)‐phosphane in the presence of AIBN. Another approach to 1‐phosphabicyclo[3.2.1]octanes involves free‐radical cyclization of 2‐methyl‐4‐(2‐propenyl)‐phospholane synthesized by the reaction of [2‐(2‐propenyl)‐4‐pentenyl]‐phosphane with KPH2/[18]crown‐6 in THF. The bicyclic phosphanes are characterized by reactions with CS2, selenium, sulfur, NO, CH3I, and HSO3F, respectively, structural and analytical data as well as 1H, 13C, 31P, 77Se NMR spectral measurements. The steric crowding of the phosphanes as complex ligands has been estimated from 31P–1H coupling constants according to the Tolman model. The configuration of the methyl substituents as well as the conformation of the six‐membered ring were determined by NMR parameters (coupling constants, noe's) and proved by X‐ray crystal structure analysis. 相似文献
14.
《化学:亚洲杂志》2017,12(1):86-94
An efficient route to the synthesis of benzo[5]helicene derivatives functionalized on the interior side of the helix was developed, and resulted in a series of 1,16‐diaryl‐substituted benzo[5]helicene derivatives starting from easily available 7‐methoxytetralone. X‐ray crystal structures showed that the benzo[5]helicene derivatives had highly helical, twisted structures, and could all create hierarchical packing architectures with alternating P and M layers in the solid state. Moreover, seven pairs of enantiomers based on 1,16‐diaryl‐substituted benzo[5]helicene derivatives were also obtained by efficient resolution through HPLC with semipreparative chiral columns. The enantiomers all showed clear mirror‐image circular dichroism (CD) spectra and high specific optical rotations, and their absolute configurations were determined by X‐ray crystallography. Interestingly, a helical nanotubular structure was formed by the self‐assembly of one enantiomer through halogen bonding. Furthermore, the enantiomers were found to have high racemization barriers and thermostability, which might be caused by the introduction of aryl substituents at the C1(C16) position. 相似文献
15.
WOLF-W. Du Mont Ralph Hensel Tevfik Severengiz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-3):73-76
Abstract Phosphanes react with tellurium much more selectively than with oxygen, sulfur and selenium. Tertiary phosphanes give “phosphane tellurides” that can equivalently be described as coordination compounds of the phosphanes with Te(O); these are kinetically labile to (phosphane) ligand substitution reactions in the nmr time scale.1 相似文献
16.
Jinyi Wang Guilin Zhuang Muqing Chen Dapeng Lu Zhe Li Qiang Huang Hongxing Jia Shengsheng Cui Xiang Shao Shangfeng Yang Pingwu Du 《Angewandte Chemie (International ed. in English)》2020,59(4):1619-1626
Carbon nanotubes (CNTs) have unusual physical properties that are valuable for nanotechnology and electronics, but the chemical synthesis of chirality‐ and diameter‐specific CNTs and π‐conjugated CNT segments is still a great challenge. Reported here are the selective syntheses, isolations, characterizations, and photophysical properties of two novel chiral conjugated macrocycles ([4]cyclo‐2,6‐anthracene; [4]CAn2,6 ), as (?)/(+)‐(12,4) carbon nanotube segments. These conjugated macrocyclic molecules were obtained using a bottom‐up assembly approach and subsequent reductive elimination reaction. The hoop‐shaped molecules can be directly viewed by a STM technique. In addition, chiral enantiomers with (?)/(+) helicity of the [4]CAn2,6 were successfully isolated by HPLC. The new tubular CNT segments exhibit large absorption and photoluminescence redshifts compared to the monomer unit. The carbon enantiomers are also observed to show strong circularly polarized luminescence (glum≈0.1). The results reported here expand the scope of materials design for bottom‐up synthesis of chiral macrocycles and enrich existing knowledge of their optoelectronic properties. 相似文献
17.
Jochanan Blum Yaron Cohen Shulamit Levin Andrea Katschak Hansruedi Glatt 《Journal of heterocyclic chemistry》1998,35(1):39-43
Racemic K-region imines of benz[a]anthracene, 7-methylbenz[a]anthracene, chrysene and benzo[a]pyrene ( 1–4 , respectively) have been resolved by high performance liquid chromatography on a column packed with amylose tris(3,5-dimethylphenylcarbamate) on silica gel. The absolute configuration of the resolved aziridines was assigned by comparison of their circular dichromism spectra to those of the corresponding enantiomerically pure arene oxides. The mutagenicity of the enantiomers of the arene imines was investigated using Salmonella typhimurium strains TA98 and TA100. Although all arene imines investigated were potent mutagens, quantitative and qualitative differences in the mutagenic activity were observed between enantiomers. 相似文献
18.
Summary Analytical HPLC methods using derivatized cellulose chiral stationary phases have been developed for separation of the enantiomers
of 25 racemic 4-aryl-7,7-dimethyl- or 1,77-trimethyl-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-diones, condensed derivatives
of dihydropyrimidines. The enantiomers of the compounds were resolved by normal-phase chromatography on silica-based cellulose
tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) and amylose tris(3,5-dimethylphenylcarbamate) (Chiralpak AD) columns with
mobile phases consisting of mixtures ofn-hexane and an alcohol (2-propanol, ethanol, or methanol) in different proportions. The mobile phase and the chiral stationary
phase were varied to achieve the best resolution. The effect of the concentration of alcohol in the mobile phase was studied.
The resolution obtained on the two columns was complementary. 相似文献
19.
A series of chiral 1,3‐dioxolanes, 3 – 12 , with >99% ee values, have been synthesized. This is the first study of chiral ketalization reaction starting from ketones with aryl, monosubstituted aryl, and long alkyl chains (C11—AC13). Their ee values were determined by chiral high‐performance liquid chromatography (HPLC) on Chiralcel OD column, using their racemic 1,3‐dioxolanes rac‐ 3 – 12 , which were also synthesized for the first time. These chiral and racemic 1,3‐dioxolanes were characterizated by infrared, NMR (1H, 13C), mass spectrometry, elemental analysis, optical rotation, and chiral HPLC. 相似文献
20.
Dr. Yasuharu Hasegawa Dr. Gerald Kehr Prof. Dr. Gerhard Erker 《Angewandte Chemie (International ed. in English)》2014,53(45):12168-12171
Bulky vinyl phosphanes undergo carbon–carbon coupling with aryl aldehydes with the help of the Lewis acid B(C6F5)3 to give isolable methylene phosphonium products. Dimesityl(vinyl)phosphane undergoes a phospha‐Stork reaction with bulky enones efficiently catalyzed by B(C6F5)3 to eventually yield the corresponding substituted cyclobutane products. 相似文献