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1.
Prof. Dr. Andreas Gansäuer Karsten Knebel Christian Kube Dr. Maurice van Gastel Asli Cangönül Prof. Dr. Kim Daasbjerg Tim Hangele Michael Hülsen Prof. Dr. Michael Dolg Dr. Joachim Friedrich 《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.
Mario Paglialunga Paradisi Giampiero Pagani Zecchini Ines Torrini Gino Lucente 《Journal of heterocyclic chemistry》1990,27(6):1661-1664
The synthesis of linear dipeptides containing N-protected L-phenylalanine and (3R-cis)-tetrahydro-1,4-thiazine-3,5-dicarboxylic acid dialkyl diester residues is described. N-Deprotection of these dipeptides by hydrogenolysis on palladium afforded directly a mixture of cis and trans dioxopiperazines. The stereochemistry and the solution conformational properties of the cyclic dipeptides are determined. 相似文献
3.
Dr. Miguel Paraja Dr. Andrea Gini Dr. Naomi Sakai Prof. Stefan Matile 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(67):15471-15476
Pnictogen-bonding catalysis and supramolecular σ-hole catalysis in general is currently being introduced as the non-covalent counterpart of covalent Lewis acid catalysis. With access to anti-Baldwin cyclizations identified as unique characteristic, pnictogen-bonding catalysis appeared promising to elucidate one of the hidden enigmas of brevetoxin-type epoxide opening polyether cascade cyclizations, that is the cyclization of certain trans epoxides into cis-fused rings. In principle, a shift from SN2- to SN1-type mechanisms could suffice to rationalize this inversion of configuration. However, the same inversion could be explained by a completely different mechanism: Ring opening with C−C bond cleavage into a branched hydroxy-5-enal and the corresponding cyclic hemiacetal, followed by cascade cyclization under conformational control, including stereoselective C−C bond formation. In this report, a pnictogen-bonding supramolecular SbV catalyst is used to demonstrate that this unorthodox polyether cascade cyclization mechanism occurs. 相似文献
4.
Dinuclear Ru–Aqua Complexes for Selective Epoxidation Catalysis Based on Supramolecular Substrate Orientation Effects
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Dr. Carlo Di Giovanni Dr. Albert Poater Dr. Jordi Benet‐Buchholz Prof. Luigi Cavallo Prof. Miquel Solà Prof. Antoni Llobet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3898-3902
Ru–aqua complex {[RuII(trpy)(H2O)]2(μ‐pyr‐dc)}+ is a powerful epoxidation catalyst for a wide range of linear and cyclic alkenes. High turnover numbers (TNs), up to 17000, and turnover frequencies (TOF), up to 24120 h?1 (6.7 s?1), have been obtained using PhIO as oxidant. This species presents an outstanding stereospecificity for both cis and trans olefins towards the formation of their corresponding cis and trans epoxides. In addition, it shows different reactivity to cis and trans olefins due to a substrate orientation supramolecular effect transmitted by its ligand scaffold. This effect together with the impressive reaction rates are rationalized using electrochemical techniques and DFT calculations. 相似文献
5.
C. R. Noe A. Weigand S. Pirker P. Liepert 《Monatshefte für Chemie / Chemical Monthly》1997,128(3):301-316
Summary Synthesis of seven new cyclic dipeptides and their conformational analysis based on1HNMR spectra is reported as well as their application as models to elucidate the mechanism of cyclic dipeptide catalysis in enantioselective mandelonitrile formation. Further evidence is presented to support the view that a highly ordered supramolecular complex of dipeptides acts as catalyst.
Untersuchungen an cyclischen Dipeptiden, 2. Mitt.: Methylierte Derivate von cyclo-[Phe-His]
Zusammenfassung Es wird die Synthese sieben neuer cyclischer Dipeptide, ihre Konformationsanalyse (basierend auf1H-NMR-Daten) und ihre Anwendung als Modelle zur Aufklärung des Mechanismus der dipeptidkatalysierten enantioselektiven Mandelsäurenitrilsynthese beschrieben. Weitere Hinweise zur Stützung der Annahme, daß ein hoch geordneter supramolekularer Komplex aus Dipeptiden für die Katalyse ausschlaggebend ist, werden vorgelegt.相似文献
6.
Light‐Induced Reversible Reconfiguration of DNA‐Based Constitutional Dynamic Networks: Application to Switchable Catalysis
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Dr. Shan Wang Dr. Liang Yue Zi‐Yuan Li Dr. Junji Zhang Prof. He Tian Prof. Itamar Willner 《Angewandte Chemie (International ed. in English)》2018,57(27):8105-8109
The light‐induced reversible and cyclic reconfiguration of constitutional dynamic networks, consisting of supramolecular nucleic acid structures as constituents and a photoisomerizable trans/cis‐azobenzene‐functionalized nucleic acid as the trigger is demonstrated. In addition, the cyclic photochemical reconfiguration of the constitutional dynamic networks guides the switchable on/off operation of an emerging hemin/G‐quadruplex DNAzyme. 相似文献
7.
Christopher Bérubé 《Supramolecular chemistry》2018,30(3):184-195
With the objective to develop supramolecular catalysts for useful chemical transformations, we report here a rapid and efficient solid-phase synthesis of novel cyclic dipeptides (crown-CDPs) with a diversity of L-DOPA derived crown ether substituents and stereochemistry. We prepared and characterized 14 crown-CDPs and evaluated their efficiency as supramolecular epoxidation catalysts in a water/hexanes biphasic system. Yields increase significantly in the presence of the crown-CDPs, though enantioselectivity depends on the nature of the substituents. The results reported constitute a useful approach for chiral epoxides of interest and further illustrate the potential of cyclic peptides as supramolecular catalysts. 相似文献
8.
Dr. Hiromitsu Sogawa Dr. Kayo Terada Yu Miyagi Prof. Dr. Masashi Shiotsuki Prof. Dr. Yoshihito Inai Prof. Dr. Toshio Masuda Prof. Dr. Fumio Sanda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(18):6747-6755
A series of new photo‐responsive amino acid‐derived azobenzenedicarboxylic acid derivatives (S)‐ 1 a – e were synthesized. Compound (S)‐ 1 a in the trans form exhibited no circular dichroism (CD) signal in DMF under ambient conditions, whereas intense Cotton effects were observed upon UV irradiation, indicating the formation of a chiral supramolecular structure in the cis form. The CD signals disappeared when trifluoroacetic acid (TFA) was added to the solution. The ester counterpart [(S)‐ 1 a′ ] showed no CD signal. Hydrogen bonding between the carboxy groups seemed necessary for constructing the supramolecular structure. The kinetic studies of cis to trans isomerization of (S)‐ 1 a demonstrated that the formation of a chiral supramolecule enhances the stability of the cis‐azobenzene structure. The ESI mass spectrum of stilbenedicarboxylic acid (S)‐ 4 , an analogue of (S)‐ 1 b , confirmed the formation of a dimer. A theoretical CD study revealed that (S)‐ 1 a in the cis form should be present as a cyclic chiral dimer. 相似文献
9.
Yanyan Zhu Mingsheng Tang Xiaoyu Shi Yufen Zhao 《International journal of quantum chemistry》2007,107(3):745-753
The preferred conformations of cyclic dipeptides were first studied systemically using the density functional theory (DFT) B3LYP method at the 6‐31G(d) level. The structural characteristics of cyclic dipeptides were revealed, most of which have not been confirmed until now. Our studies showed that the six‐member main circles of cyclic dipeptides composed of natural L ‐amino acid residues appeared as boat conformations. The important factors that influence conformations of cyclic dipeptides, such as molecular total energy, nuclear repulsion energy, molecular orbit, spatial effects, and reactive mechanism, are discussed in detail. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
10.
Bhawani Narayan Karteek K. Bejagam Sundaram Balasubramanian Subi J. George 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(44):13245-13249
A “chirality driven self‐sorting” strategy is introduced for the controlled supramolecular organization of donor (D) and acceptor (A) molecules in multicomponent assemblies. The trans‐1,2‐bis(amido)cyclohexane (trans‐BAC) has been identified as a supramolecular motif with strong homochiral recognition to direct this chirality controlled assembly process of enantiomers in solution. Stereoselective supramolecular polymerization of trans‐BAC appended naphthalene diimide monomers (NDIs) has been probed in detail by spectroscopic and mechanistic investigations. This chirality‐driven self‐sorting design of enantiomeric components also offers to realize mixed and segregated D‐A stacks by supramolecular co‐assembly of the NDI acceptors with trans‐BAC appended dialkoxynaphthalene (DAN) donor monomers. Such an unprecedented chirality control on D‐A organization paves the way for the creation of supramolecular p‐n nanostructures with controlled molecular‐level organization. 相似文献
11.
Mohammad Navid Soltani Rad Ali Khalafi-Nezhad Somayeh Behrouz Zohreh Amini Marzieh Behrouz 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1658-1671
A facile and highly efficient method for one-pot Beckmann rearrangement of ketoximes into N-substituted amides using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, ketoximes are refluxed with TsIm and Cs2CO3 in the presence of SiO2 as a recyclable catalyst in DMF affording the corresponding amides in high yields. This methodology is highly efficient and regioselective for various structurally diverse ketoximes including symmetrical and unsymmetrical as well as cyclic oximes. The results of quantum mechanical studies used to rationalize the experimental outcomes are discussed. 相似文献
12.
Dr. Abhishek Dutta Chowdhury Dr. Nico Weding Dr. Jennifer Julis Prof. Dr. Robert Franke Dr. Ralf Jackstell Prof. Dr. Matthias Beller 《Angewandte Chemie (International ed. in English)》2014,53(25):6477-6481
The efficient catalytic dehydrogenation of alkanes to olefins is one of the most investigated reactions in organic synthesis. In the coming years, an increased supply of shorter‐chain alkanes from natural and shale gas will offer new opportunities for inexpensive carbon feedstock through such dehydrogenation processes. Existing methods for alkane dehydrogenation using heterogeneous catalysts require harsh reaction conditions and have a lack of selectivity, whereas homogeneous catalysis methods result in significant waste generation. A strong need exists for atom‐efficient alkane dehydrogenations on a useful scale. Herein, we have developed improved acceptorless catalytic systems under optimal light transmittance conditions using trans‐[Rh(PMe3)2(CO)Cl] as the catalyst with different additives. Unprecedented catalyst turnover numbers are obtained for the dehydrogenation of cyclic and linear (from C4) alkanes and liquid organic hydrogen carriers. These reactions proceed with unique conversion, thereby providing a basis for practical alkane dehydrogenations. 相似文献
13.
Diastereoselectively Switchable Asymmetric Haloaminocyclization for the Synthesis of Cyclic Sulfamates
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Dr. Yunfei Cai Pengfei Zhou Prof. Dr. Xiaohua Liu Jiannan Zhao Dr. Lili Lin Prof. Dr. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6386-6389
An asymmetric synthesis of cyclic sulfamates by catalytic haloaminocyclization of primary sulfamate ester derivatives is described. The remarkable reversal of diastereoselectivity was found to be dependent on the halogen source and the chiral catalyst. By using privileged complexes of N,N′‐dioxides with Sc(OTf)3 or Lu(OTf)3 as the catalyst, a variety of enantioenriched syn‐ and anti‐cyclic sulfamates or related trans‐aziridines could be obtained in 92–99 % ee and up to 97 % yield. 相似文献
14.
Although supramolecular one‐dimensional (1D) and two‐dimensional (2D) structures with various unique properties have been extensively studied, the reversible switching between tubules and sheets via lateral association remains challenging. Here, we report the unique structures of a supramolecular tubular bamboo culm in which the hollow‐tubular interior is separated, at intervals, by nodes per 1.3 nm. Interestingly, the discrete tubules are able to hierarchically assemble into a flat sheet in response to an aromatic guest. The addition of trans‐azobenzene, as a guest, enables the tubules to form a hierarchical sheet assembly via the lateral interaction. The hierarchical sheet structures are disassembled into their constituent tubules upon UV irradiation due to trans‐cis isomerization. The recovery from cis‐azobenzene to trans‐form induces repeatedly the hierarchical sheet assembly, indicative of a reversible switching behavior between tubules and sheets triggered by an external stimulus. 相似文献
15.
Christopher Bérubé 《合成通讯》2016,46(5):395-403
We have developed a practical epoxidation of electron-deficient enones in aqueous media using cyclic dipeptides as bioinspired green catalyst. Optimizing the reaction conditions in a triphasic system led to efficient conditions providing epoxides with good enantioselectivities. Depending on the catalyst substituent chirality, both enantiomers are obtained. The cyclic rigidity impacts significantly the enantioselectivity. 相似文献
16.
Dr. Renat Kadyrov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):1002-1012
An efficient procedure is described for ring‐closing metathesis reactions. A conversion of 95 % for diethyl diallylmalonate in dilute solution could be achieved within a few minutes, reaching TOF=4173 min?1, with very low loading of commercially available Ru catalysts that contained unsaturated NHC ligands. In general, only 50 to 250 ppm of the catalyst is required to achieve near‐quantitative conversion into a broad variety of 5–16‐membered heterocyclic compounds. The practicality of this procedure was illustrated in the synthesis of 5–8‐membered N‐tert‐butoxycarbonyl (N‐Boc)‐ and N‐para‐toluenesulfonyl (N‐Ts)‐protected cyclic amines and 9–16‐membered lactones. The synthesis of macrocyclic proline‐based lactams required slightly higher catalyst loadings. Along with monocyclic products, oligomeric byproducts, mostly cyclodimers, were isolated and characterized. 相似文献
17.
Summary Seven new cyclic dipeptides have been synthesized and tested for their applicability as tools to elucidate the mechanism of formation of mandelonitrile with (SS)-cyclo-[Phe-His] type catalysts. Conformational analyses based on1H NMR spectra are presented for all prepared cyclic dipeptides.Dedicated to Prof. Dr. Dres. h.c.Herbert Oelschläger on the occasion of his 75th birthday 相似文献
18.
A 3,4‐trans‐Fused Cyclic Protecting Group Facilitates α‐Selective Catalytic Synthesis of 2‐Deoxyglycosides
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Dr. Edward I. Balmond Dr. David Benito‐Alifonso Dr. Diane M. Coe Prof. Roger W. Alder Dr. Eoghan M. McGarrigle Dr. M. Carmen Galan 《Angewandte Chemie (International ed. in English)》2014,53(31):8190-8194
A practical approach has been developed to convert glucals and rhamnals into disaccharides or glycoconjugates with high α‐selectivity and yields (77–97 %) using a trans‐fused cyclic 3,4‐O‐disiloxane protecting group and TsOH?H2O (1 mol %) as a catalyst. Control of the anomeric selectivity arises from conformational locking of the intermediate oxacarbenium cation. Glucals outperform rhamnals because the C6 side‐chain conformation augments the selectivity. 相似文献
19.
l-Proline-based cyclic dipeptides were synthesized from N-Boc-protected dipeptide methyl esters under catalyst-free condition using water as a solvent. One-pot deprotection and cyclization have been used as the key steps, providing an efficient and environmentally friendly approach. Clean reaction conditions, easy isolation, and good yields of cyclic dipeptides are the salient features of the proposed methodology. 相似文献
20.
Dr. Johannes Großkopf Dr. Manuel Plaza Dr. Roger Jan Kutta Prof. Dr. Patrick Nuernberger Prof. Dr. Thorsten Bach 《Angewandte Chemie (International ed. in English)》2023,62(47):e202313606
2,5-Diketopiperazines are cyclic dipeptides displaying a wide range of applications. Their enantioselective preparation has now been found possible from the respective racemates by a photochemical deracemization (53 examples, 74 % to quantitative yield, 71–99 % ee). A chiral benzophenone catalyst in concert with irradiation at λ=366 nm enables to establish the configuration at the stereogenic carbon atom C6 at will. If other stereogenic centers are present in the diketopiperazines they remain unaffected and a stereochemical editing is possible at a single position. Consecutive reactions, including the conversion into N-aryl or N-alkyl amino acids or the reduction to piperazines, occur without compromising the newly created stereogenic center. Transient absorption spectroscopy revealed that the benzophenone catalyst processes one enantiomer of the 2,5-diketopiperazines preferentially and enables a reversible hydrogen atom transfer that is responsible for the deracemization process. The remarkably long lifetime of the protonated ketyl radical implies a yet unprecedented mode of action. 相似文献