共查询到20条相似文献,搜索用时 15 毫秒
1.
Ferdinand Krner Markus Schürmann Hans Preut Wolfgang Kreiser 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):76-77
Esterification of a single diastereomer of 2‐(4‐methylenecyclohex‐2‐enyl)propanol, (II), with (1R,4S)‐(+)‐camphanic acid [(1R,4S)‐4,7,7‐trimethyl‐3‐oxo‐2‐oxabicyclo[2.2.1]heptane‐1‐carboxylic acid] leads to the crystalline title compound, C20H28O4. The relative configuration of the camphanate was determined by X‐ray diffraction analysis. The outcome clarifies the relative and absolute stereochemistry of the naturally occurring bisabolane sesquiterpenes β‐turmerone and β‐sesquiphellandrene, since we have converted (II) into both natural products via a stereospecific route. 相似文献
2.
Zi‐Qiang Hu Duan‐Jun Xu Yuan‐Zhi Xu Jing‐Yun Wu Michael Y. Chiang 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(10):o612-o614
Crystals of the title complex, C3H7NO2·C8H8O3·0.5H2O, were obtained from an aqueous solution containing racemic mandelic acid and (S)‐alanine. The unit cell includes two independent molecular complexes and one water molecule. The structure formed by (R)‐mandelic acid and (S)‐alanine in a 1:1 molar ratio shows the successful optical separation of racemic mandelic acid. Strong hydrogen bonding, with a rather short O?O separation of 2.494 (3) Å, is observed between the carboxyl and carboxylate groups. A structural comparison suggests that the strong hydrogen bonding affects the neighbouring covalent bond. 相似文献
3.
Huub Kooijman Anthony L. Spek Henk Kleijn Hendrik L. van Maanen Johann T. B. H. Jastrzebski Gerard van Koten 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):481-483
The configuration of the chiral ring atoms of the title compound, C26H26N2O, obtained in an enantioselective synthesis, has been established relative to the known R configuration of the α‐methylbenzyl moieties. The crystal packing involves a two‐dimensional network of C—H?π interactions between the aromatic rings. 相似文献
4.
Saúl Torres Manuel Velasco Jos ngel Gallegos‐Rojas Sylvain Berns María L. Orea Joel L. Tern Gabriela Huelgas Víctor Gmez‐Calvario Jorge R. Jurez 《Journal of heterocyclic chemistry》2019,56(9):2677-2682
We describe here an efficient stereoselective method for the preparation of (R)‐2‐benzylmorpholine and ML398. The present method features a high diastereocontrol using an endocyclic oxidation of phenylglycinol‐derived morpholine and a stereoselective alkylation of chiral non‐racemic morpholin‐3‐one as key steps. 相似文献
5.
Christopher S. Frampton David D. MacNicol Derek R. Wilson 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(5):o188-o191
The title compounds, C18H21NO and C18H21NS, in their enantiomerically pure forms are isostructural with the enantiomerically pure 4‐(4‐hydroxyphenyl)‐2,2,4‐trimethylchroman and 4‐(2,4‐dihydroxyphenyl)‐2,2,4‐trimethylchroman analogues and form extended linear chains via N—H...O or N—H...S hydrogen bonding along the [100] direction. The absolute configuration for both compounds was determined by anomalous dispersion methods with reference to both the Flack parameter and, for the light‐atom compound, Bayesian statistics on Bijvoet differences. 相似文献
6.
7.
Takashi Sugimoto Kazuhisa Ikemoto Shizuaki Murata Masahiro Tazawa Takahide Nomura Yasumichi Hagino Hiroshi Ichinose Toshiharu Nagatsu 《Helvetica chimica acta》2001,84(4):918-927
The structure of the native pteridine in Tetrahymena pyriformis was determined as (6R)‐5,6,7,8‐tetrahydro‐D ‐monapterin (=(6R)‐2‐amino‐5,6,7,8‐tetrahydro‐6‐[(1R,2R)‐1,2,3‐trihydroxypropyl]pteridin‐4(3H)‐one; 4 ). First, the configuration of the 1,2,3‐trihydroxypropyl side chain was confirmed as D ‐threo by the fluorescence‐detected circular dichroism (FDCD) spectrum of its aromatic pterin derivative 2 obtained by I2 oxidation (Fig. 1). The configuration at the 6‐position of 4 was determined as (R) by comparison of its hexaacetyl derivative 6 with authentic (6R)‐ and (6S)‐hexaacetyl‐5,6,7,8‐tetrahydro‐D ‐monapterins 6 and 7 , respectively, in the HPLC, LC/MS, and LC‐MS/MS (Figs. 3 – 6). (6R)‐5,6,7,8‐Tetrahydro‐D ‐monapterin ( 4 ) is a newly discovered natural tetrahydropterin. 相似文献
8.
9.
Kinkini Bhattacharyya Tanusree Kar Rex A. Palmer Brian S. Potter Akira Inada 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(8):979-980
In the title compound, C30H50O3, the three six‐membered rings adopt chair, twist and twist‐boat conformations. The five‐membered ring is in a slightly distorted envelope conformation. The substituent on the five‐membered ring is in an extended conformation, with its two hydroxyl O atoms forming an intramolecular hydrogen bond. One of these O atoms also forms an intermolecular hydrogen bond with the oxygen of the carbonyl group in a neighbouring molecule. 相似文献
10.
Ferdinand Krner Markus Schürmann Hans Preut Wolfgang Kreiser 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):74-75
Stereoselective hydroboration of (?)‐isopulegol and subsequent fractional crystallization furnishes the title compound, C10H20O2. The relative configuration of the stereogenic centres has been assigned by means of X‐ray diffraction analysis since the monoterpenediol is employed as a versatile chiral building block in stereospecific natural product synthesis. 相似文献
11.
Zhongtao Wu Prof. Dr. Syuzanna R. Harutyunyan Prof. Dr. Adriaan J. Minnaard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14250-14255
Based on the asymmetric copper‐catalyzed 1,2‐addition of Grignard reagents to ketones, (R,R,R)‐γ‐tocopherol has been synthesized in 36 % yield over 12 steps (longest linear sequence). The chiral center in the chroman ring was constructed with 73 % ee by the 1,2‐addition of a phytol‐derived Grignard reagent to an α‐bromo enone prepared from 2,3‐dimethylquinone. 相似文献
12.
Dr. Andreas Ole Termath B. Sc. Hanna Sebode M. Sc. Waldemar Schlundt Dr. René T. Stemmler Dr. Thomas Netscher Priv.‐Doz. Dr. Werner Bonrath Prof. Dr. Hans‐Günther Schmalz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12051-12055
By introducing a disposable activating substituent at C‐3, the asymmetric 1,4‐addition to a notoriously unreactive 2‐substituted chromenone was achieved with high levels of (2R)‐stereoselectivity in the presence of a chiral CuI‐phosphoramidite complex as a catalyst. This paved the way for an efficient and conceptually novel synthesis of (R,R,R)‐α‐tocopherol from readily available starting materials. 相似文献
13.
Li Qin Qiu Jian Ying Qi Jian Xin Ji Zhong Yuan Zhou Chi Hung Yeung Michael C. K. Choi Albert S. C. Chan 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(1):o33-o35
The title compound, C36H28O4P2·CH4O, was synthesized directly from the methoxy analogue. The crystal structure shows that one OH group interacts with an O atom of a phosphine oxide group in an adjacent molecule, while the other OH group complexes with the methanol solvent molecule via intermolecular hydrogen bonds. An O atom of one phosphine oxide group interacts with the hydroxy H atom of methanol via a hydrogen bond. There are intra‐ and intermolecular π–π interactions between the phenyl rings. All these interactions result in the formation of supramolecular chiral parallelogram channels via self‐assembly. 相似文献
14.
Chun‐Hua Diao Zhi Fan Xin Chen 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(12):o717-o719
In the title compound, C21H18ClN3O5S·C2H4O2, a combination of O—H...O, N—H...O, C—H...O and C—H...N hydrogen bonds links the components into a complex network containing alternating R44(42), R55(33) and R66(40) rings. 相似文献
15.
A simple and efficient enantioselective synthesis of chromene, (?)‐(R)‐cordiachromene ( 1 ), and (?)‐(R)‐dictyochromenol ( 2 ) has been accomplished. This convergent synthesis utilizes intramolecular SNAr reaction for the formation of chroman ring, and Seebach's method of ‘self‐reproduction of chirality’ should establish the (R)‐configuration of the C(2) side chain as key steps. 相似文献
16.
Yingxin Xiao Ronald J. Voll Damon R. Billodeaux Frank R. Fronczek Ezzat S. Younathan 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):582-583
The title compound, C20H22O6, has crystallographic twofold symmetry. The central six‐C‐atom chain has an extended conformation similar to that of d ‐mannitol, with two independent C—C—C—C torsion angles of 165.69 (14) and 177.60 (12)°. The 1,3‐dioxane ring has a chair conformation. All chiral centers have the R configuration. 相似文献
17.
Péter Király Tibor Soós Szilárd Varga Benedek Vakulya Gábor Tárkányi 《Magnetic resonance in chemistry : MRC》2010,48(1):13-19
The conformational diversity of the (3R,4S,8R,9R)‐9‐[(3,5‐bis(trifluoromethyl)phenyl))‐thiourea](9‐deoxy)‐epi‐cinchonine organocatalyst is discussed. Low‐temperature NMR experiments confirmed a self‐association process, which promotes the quinoline rotation between two intramolecularly hydrogen‐bonded monomeric conformers of the catalyst. The balanced population of the coexisting monomeric and dimeric species allowed us to conduct a structural study of a rather complex conformational dynamics of the pure catalyst. The study is extended by a comparison with other members of the bifunctional amine‐thiourea organocatalyst family. Changes in the molecular structure of the catalysts influence the interplay between intra‐ and intermolecular hydrogen bonding, and yield different extent of catalyst self‐association. By assessing the conformation of the individual states, we established the thermodynamic model of a self‐association promoted conformational transition. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
18.
Pter Molnr Jzsef Deli Erzsbet sz Ferenc Zsila Mikls Simonyi Gyula Tth 《Helvetica chimica acta》2004,87(8):2159-2168
Circular dichroism (CD) spectroscopy was used to distinguish between the isomeric (all‐E)‐configured 3′‐epilutein ( 2 ) and 6′‐epilutein ( 8 ) to establish the absolute configuration of epilutein samples of different (natural and semisynthetic) origin, including samples of 2 obtained from thermally processed sorrel. Thus, the CD data of lutein ( 1 ) and epilutein samples ( 2 ) were compared. Our results unambiguously confirmed the (3R,3′S,6′R)‐configuration of all epilutein samples. Compound 2 was thoroughly characterized, and its 13C‐NMR data are published herewith for the first time. 相似文献
19.
Marian Koman Peter Szolcsnyi Tibor Gracza 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(4):e138-e138
The absolute configuration at the new stereogenic centre during the key step of the total synthesis was established byX‐ray analysis of the title compound, C7H15NO4+·Cl?. 相似文献
20.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(6):1571-1574
The enantioselective total synthesis of (−)‐tetrodotoxin [(−)‐TTX] and 4,9‐anhydrotetrodotoxin, which are selective blockers of voltage‐gated sodium channels, was accomplished from the commercially available p ‐benzoquinone. This synthesis was based on efficient stereocontrol of the six contiguous stereogenic centers on the core cyclohexane ring through Ogasawara's method, [3,3]‐sigmatropic rearrangement of an allylic cyanate, and intramolecular 1,3‐dipolar cycloaddition of a nitrile oxide. Our synthetic route was applied to the synthesis of the tetrodotoxin congeners 11‐norTTX‐6(R )‐ol and 4,9‐anhydro‐11‐norTTX‐6(R )‐ol through late‐stage modification of the common intermediate. Neutral deprotection at the final step enabled easy purification of tetrodotoxin and 11‐norTTX‐6(R )‐ol without competing dehydration to their 4,9‐anhydro forms. 相似文献