446 results found
Rzepa HS, Kuhn S, 2021, A data-oriented approach to making new molecules as a student experiment: artificial intelligence-enabling FAIR publication of NMR data for organic esters, MAGNETIC RESONANCE IN CHEMISTRY, ISSN: 0749-1581
Rzepa HS, 2021, The Long and Winding Road towards FAIR Data as an Integral Component of the Computational Modelling and Dissemination of Chemistry, ISRAEL JOURNAL OF CHEMISTRY, ISSN: 0021-2148
Rzepa HS, 2021, Routes involving no free C-2 in a DFT-computed mechanistic model for the reported room-temperature chemical synthesis of C-2, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 23, Pages: 12630-12636, ISSN: 1463-9076
Alamillo-Ferrer C, Nielsen CD-T, Salzano A, et al., 2021, Understanding the Diastereopreference of Intermediates in Aminocatalysis: Application to the Chiral Resolution of Lactols, JOURNAL OF ORGANIC CHEMISTRY, Vol: 86, Pages: 4326-4335, ISSN: 0022-3263
Rzepa HS, 2021, A thermodynamic assessment of the reported room-temperature chemical synthesis of C-2, NATURE COMMUNICATIONS, Vol: 12, ISSN: 2041-1723
Bachrach SM, Rzepa HS, 2020, Cycloparaphenylene Mobius trefoils, CHEMICAL COMMUNICATIONS, Vol: 56, Pages: 13567-13570, ISSN: 1359-7345
Yildiz CB, Leszczynska KI, Gonzalez-Gallardo S, et al., 2020, Equilibrium Formation of Stable All-Silicon Versions of 1,3-Cyclobutanediyl, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 59, Pages: 15087-15092, ISSN: 1433-7851
Yildiz CB, Leszczyńska KI, González-Gallardo S, et al., 2020, Bildung Stabiler All-Silicium Varianten von 1,3-Cyclobutandiyl im Gleichgewicht, Angewandte Chemie, Vol: 132, Pages: 15199-15204, ISSN: 0044-8249
Sebest F, Lachhani K, Pimpasri C, et al., 2020, Cycloaddition reactions of azides and electron-deficient alkenes in deep eutectic solvents: pyrazolines, aziridines and other surprises, Advanced Synthesis & Catalysis, Vol: 362, Pages: 1877-1886, ISSN: 1615-4150
The reaction of organic azides and electron‐deficient alkenes was investigated in a deep eutectic solvent. A series of highly substituted 2‐pyrazolines was successfully isolated and their formation rationalised by DFT calculations. The critical effect of substitution was also explored; even relatively small changes in the cycloaddition partners led to completely different reaction outcomes and triazolines, triazoles or enaminones can be formed as major products depending on the alkene employed.
Klein JEMN, Knizia G, Rzepa HS, 2019, Epoxidation of Alkenes by Peracids: From Textbook Mechanisms to a Quantum Mechanically Derived Curly-Arrow Depiction, CHEMISTRYOPEN, Vol: 8, Pages: 1244-1250, ISSN: 2191-1363
Shernyukov AV, Genaev AM, Salnikov GE, et al., 2019, Elevated reaction order of 1,3,5-tri-tert-butylbenzene bromination as evidence of a clustered polybromide transition state: a combined kinetic and computational study, ORGANIC & BIOMOLECULAR CHEMISTRY, Vol: 17, Pages: 3781-3789, ISSN: 1477-0520
Du Y, Barber T, Lim SE, et al., 2019, A solid-supported arylboronic acid catalyst for direct amidation, CHEMICAL COMMUNICATIONS, Vol: 55, Pages: 2916-2919, ISSN: 1359-7345
Barba A, Dominguez S, Gomez C, et al., 2019, Workflows allowing creation of journal article Supporting Information and FAIR-enabled publication of Spectroscopic data, ACS Omega, Vol: 4, Pages: 3280-3286, ISSN: 2470-1343
There is an increasing focus on the part of academic institutions, funding agencies, and publishers, if not researchers themselves, on preservation and sharing of research data. Motivations for sharing include research integrity, replicability, and reuse. One of the barriers to publishing data is the extra work involved in preparing data for publication once a journal article and its supporting information have been completed. In this work, a method is described to generate both human and machine-readable supporting information directly from the primary instrumental data files and to generate the metadata to ensure it is published in accordance with findable, accessible, interoperable, and reusable (FAIR) guidelines. Using this approach, both the human readable supporting information and the primary (raw) data can be submitted simultaneously with little extra effort. Although traditionally the data package would be sent to a journal publisher for publication alongside the article, the data package could also be published independently in an institutional FAIR data repository. Workflows are described that store the data packages and generate metadata appropriate for such a repository. The methods both to generate and to publish the data packages have been implemented for NMR data, but the concept is extensible to other types of spectroscopic data as well.
Sebest F, Casarrubios L, Rzepa HS, et al., 2018, Thermal Azide-Alkene Cycloaddition Reactions: Straightforward Multi-gram Access to Δ²-1,2,3-Triazolines in Deep Eutectic Solvents, Green Chemistry, Vol: 20, Pages: 4023-4035, ISSN: 1463-9262
The multi-gram synthesis of a wide range of 1,2,3-triazolines via azide–alkene cycloaddition reactions in a Deep Eutectic Solvent (DES) is reported. The role of DES in this transformation as well as the origin of the full product distribution was studied with an experimental/computational-DFT approach.
Rzepa HS, Arkhipenko S, Wan E, et al., 2018, An accessible method for DFT calculation of B-11 NMR shifts of organoboron compounds, Journal of Organic Chemistry, Vol: 83, Pages: 8020-8025, ISSN: 0022-3263
The study of boron-mediated reactions in organic synthesis and reactions of organoboron compounds is greatly facilitated by the use of 11B NMR. However, the identification and characterization of reaction intermediates in often complex systems is far from trivial, as 11B NMR does not provide any detailed structural information. Greater insight into the structures present in such systems can be obtained by using DFT chemical shift calculations to support or exclude proposed reaction intermediates. In this article, we report a rapid and accessible approach to the calculation of 11B NMR shifts that is applicable to a wide range of organoboron compounds.
Mandal D, Dhara D, Maiti A, et al., 2018, Mono- and Dicoordinate Germanium(0) as a Four-Electron Donor, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 24, Pages: 2873-2878, ISSN: 0947-6539
Arkhipenko S, Sabatini MT, Batsanov AS, et al., 2018, Mechanistic insights into boron-catalysed direct amidation reactions, Chemical Science, Vol: 9, Pages: 1058-1072, ISSN: 2041-6520
The generally accepted monoacyloxyboron mechanism of boron-catalysed direct amidation is brought into question in this study, and new alternatives are proposed. We have carried out a detailed investigation of boron-catalysed amidation reactions, through study of the interaction between amines/carboxylic acids and borinic acids, boronic acids and boric acid, and have isolated and characterised by NMR/X-ray crystallography many of the likely intermediates present in catalytic amidation reactions. Rapid reaction between amines and boron compounds was observed in all cases, and it is proposed that such boron–nitrogen interactions are highly likely to take place in catalytic amidation reactions. These studies also clearly show that borinic acids are not competent catalysts for amidation, as they either form unreactive amino-carboxylate complexes, or undergo protodeboronation to give boronic acids. It therefore seems that at least three free coordination sites on the boron atom are necessary for amidation catalysis to occur. However, these observations are not consistent with the currently accepted ‘mechanism’ for boron-mediated amidation reactions involving nucleophilic attack of an amine onto a monomeric acyloxyboron intermediate, and as a result of our observations and theoretical modelling, alternative proposed mechanisms are presented for boron-mediated amidation reactions. These are likely to proceed via the formation of a dimeric B–X–B motif (X = O, NR), which is uniquely able to provide activation of the carboxylic acid, whilst orchestrating the delivery of the amine nucleophile to the carbonyl group. Quantum mechanical calculations of catalytic cycles at the B3LYP+D3/Def2-TZVPP level (solvent = CH2Cl2) support the proposal of several closely related potential pathways for amidation, all of which are likely to be lower in energy than the currently accepted mechanism.
Davies AN, Martinsen D, Rzepa HS, et al., 2017, Simplifying spectroscopic supplementary data collection, Spectroscopy Europe, Vol: 29, Pages: 6-10, ISSN: 0966-0941
Almond-Thynne J, White AJP, Polyzos A, et al., 2017, Synthesis and reactions of benzannulated spiroaminals: tetrahydrospirobiquinolines, ACS Omega, Vol: 2, Pages: 3241-3249, ISSN: 2470-1343
An efficient two-step synthesis of symmetrical and unsymmetrical tetrahydrospirobiquinolines from o-azidobenzaldehydes is reported. A novel series of tetrahydrospirobiquinolines was prepared by sequential double-aldol condensation with acetone, cyclopentanone, and cyclohexanone to form the corresponding o,o′-diazido-dibenzylidene-acetone, -cyclopentanone, and -cyclohexanone derivatives, respectively, and hydrogenation–spirocyclization. The spirodiamines were further derivatized by electrophilic aromatic bromination, Suzuki coupling, and N-alkylation, all of which proceeded with preservation of the spirocyclic core.
Abas H, Linsdall SM, Mamboury M, et al., 2017, Total Synthesis of (+)-Lophirone H and Its pentamethyl ether utilizing an oxonium-prins cyclization, Organic Letters, Vol: 19, Pages: 2486-2489, ISSN: 1523-7052
The first total synthesis of (+)-lophirone H (1) and its pentamethyl ether 29, featuring an oxonium–Prins cyclization/benzylic cation trapping reaction, is described.
Murray JI, Flodén NJ, Bauer A, et al., 2017, Kinetic Resolution of 2-Substituted Indolines by N -Sulfonylation using an Atropisomeric 4-DMAP- N -oxide Organocatalyst, Angewandte Chemie, Vol: 129, Pages: 5854-5858, ISSN: 0044-8249
The first catalytic kinetic resolution by N‐sulfonylation is described. 2‐Substituted indolines are resolved (s=2.6–19) using an atropisomeric 4‐dimethylaminopyridine‐N‐oxide (4‐DMAP‐N‐oxide) organocatalyst. Use of 2‐isopropyl‐4‐nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.
Murray JI, Floden NJ, Bauer A, et al., 2017, Kinetic resolution of 2-substituted indolines by N-sulfonylation using an atropisomeric 4-DMAP-N-oxide organocatalyst, Angewandte Chemie International Edition, Vol: 56, Pages: 5760-5764, ISSN: 1433-7851
The first catalytic kinetic resolution by N-sulfonylation is described. 2-Substituted indolines are resolved (s=2.6–19) using an atropisomeric 4-dimethylaminopyridine-N-oxide (4-DMAP-N-oxide) organocatalyst. Use of 2-isopropyl-4-nitrophenylsulfonyl chloride is critical to the stereodiscrimination and enables facile deprotection of the sulfonamide products with thioglycolic acid. A qualitative model that accounts for the stereodiscrimination is proposed.
May PW, Cotton SA, Harrison K, et al., 2017, The 'Molecule of the Month' Website-An Extraordinary Chemistry Educational Resource Online for over 20 Years, MOLECULES, Vol: 22, ISSN: 1420-3049
Rzepa HS, Harvey MJ, Mclean A, 2017, A metadata-driven approach to data repository design, Journal of Cheminformatics, Vol: 9, ISSN: 1758-2946
The design and use of a metadata-driven data repository for research data management is described. Metadata is collectedautomatically during the submission process whenever possible and is registered with DataCite in accordancewith their current metadata schema, in exchange for a persistent digital object identifier. Two examples of data previeware illustrated, including the demonstration of a method for integration with commercial software that confersrich domain-specific data analytics without introducing customisation into the repository itself.
Calbo J, Weston CE, White A, et al., 2016, Tuning azoheteroarene photoswitch performance through heteroaryl design, Journal of the American Chemical Society, Vol: 139, Pages: 1261-1274, ISSN: 1520-5126
Photoswitchable compounds, which can be reversibly switched between two isomers by light, continue to attract significant attention for a wide array of applications. Azoheteroarenes represent a relatively new but understudied type of photoswitch, where one of the aryl rings from the conventional azobenzene class has been replaced with a five-membered heteroaromatic ring. Initial studies have suggested the azoheteroarenes - the arylazopyrazoles in particular - to have excellent photoswitching properties (quantitative switching and long Z isomer half-life). Here we present a systematic computational and experimental study to elucidate the origin of the long thermal half-lives and excellent addressability of the arylazopyrazoles, and apply this understanding to determine important structure-property relationships for a wide array of comparable azoheteroaryl photoswitches. We identify compounds with Z isomer half-lives ranging from seconds to hours, to days and to years, and variable absorption characteristics; all through tuning of the heteraromatic ring. Conformation perhaps plays the largest role in determining such properties; where the compounds with the longest isomerization half-lives adopt a T-shaped ground state Z isomer conformation and proceed through a T-shaped isomerization pathway, whereas the most complete photoswitching is achieved for compounds that have a twisted (rather than T-shaped) Z-isomer conformation. By balancing these factors, we report a new azopyrazole 3pzH, which can be quantitatively switched to its Z-isomer (>98%) with 355 nm irradiation, near-quantitatively (97%) switched back to the E isomer with 532 nm irradiation, and has a very long half-life for thermal isomerisation (t1/2 = 74 d at 25 °C). Given the large tunability of their properties, the predictive nature of their performance, and the other functional opportunities afforded by usage of a heteroaromatic system, we believe the azoheteroaryl photoswitches to have huge potent
Braddock DC, Rzepa HS, Clarke J, et al., 2016, Epimeric Face-Selective Oxidations and Diastereodivergent Transannular Oxonium Ion Formation Fragmentations: Computational Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D, Journal of Organic Chemistry, Vol: 81, Pages: 9539-9552, ISSN: 1520-6904
The total synthesis of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C and marilzabicycloallene D as halogenated C15-acetogenin twelve-membered bicyclic and tricyclic ether bromoallene-containing marine metabolites from Laurencia species are described. Two enantiomerically pure C4-epimeric dioxabicyclo[8.2.1]tridecenes were synthesised by E-selective ring-closing metathesis where their absolute stereochemistry was previously set via catalytic asymmetric homoallylic epoxidation and elaborated via regioselective epoxide-ring opening and diastereoselective bromoetherification. Epimeric face-selective oxidation of their Δ12,13 olefins followed by bromoallene installation allowed access to the oppositely configured 12,13-epoxides of 12-epoxyobtusallene II & 12-epoxyobtusallene IV. Subsequent exploration of their putative biomimetic oxonium ion formation-fragmentations reactions revealed diastereodivergent pathways giving marilzabicycloallene C and obtusallene X respectively. The original configurations of the substrates evidently control oxonium ion formation and their subsequent preferred mode of fragmentation by nucleophilic attack at C9 or C12. Quantum modelling of this stereoselectivity at the ωB97X-D/Def2-TZVPPD/SCRF=methanol level revealed that in addition to direction resulting from hydrogen bonding, the dipole moment of the ion-pair transition state is an important factor. Marilzabicycloallene D as a pentahalogenated twelve-membered bicyclic ether bromoallene was synthesised by a face-selective chloronium ion initiated oxonium ion formation-fragmentation process followed by subsequent bromoallene installation.
The first stable bromoallene oxides were obtained by the DMDO epoxidation of 1-bromo-1,3-di-tert-alkylallenes, producing the first crystalline allene oxide of any kind. The epoxidations are regioselective for the bromine-bearing Δ1,2 alkene, and also face selective producing single diastereomer E-olefin products.
Andrade MS, Silva VS, Lourenco AM, et al., 2016, Chiroptical Properties of Streptorubin B: The Synergy Between Theory and Experiment (vol 27, pg 745, 2015), CHIRALITY, Vol: 28, Pages: 663-663, ISSN: 0899-0042
Romain C, Zhu Y, Dingwall P, et al., 2016, Chemoselective polymerizations from mixtures of epoxide, lactone, anhydride, and carbon dioxide, Journal of the American Chemical Society, Vol: 138, Pages: 4120-4131, ISSN: 1520-5126
Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymeri-zation (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers: -caprolactone, cyclohexene oxide, phthalic anhydride and carbon dioxide are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity resulting in block sequence control and predictable compositions (esters and car-bonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically con-trolled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.
Rzepa HS, 2016, Discovering More Chemical Concepts from 3D Chemical Information Searches of Crystal Structure Databases, JOURNAL OF CHEMICAL EDUCATION, Vol: 93, Pages: 550-554, ISSN: 0021-9584
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