120 results found
Braddock D, Rowley B, Lickiss P, et al., 2023, On the use of triarylsilanols as catalysts for direct amidation of carboxylic acids, Journal of Organic Chemistry, Vol: 88, Pages: 9853-9869, ISSN: 0022-3263
Triarylsilanols are reported as the first silicon-centred molecular catalysts for direct amidation of carboxylic acids with amines as identified after a screen of silanols, silanediols, disiloxanediols and incompletely condensed silsesquioxanes as potential homogeneous catalysts. Subsequent synthesis and testing of various electronically differentiated triarylsilanols identify tris(p-haloaryl)silanols as more active than the parent triarylsilanol, where the bromide congener was found to be the most active. Catalyst decomposition can be observed by NMR methods, but RPKA methods reveal that product inhibition is operative, where tertiary amides are more inhibitory than secondary amides. Studies using an authentically synthesised triaryl silylester as a putative intermediate in the catalytic system enable a plausible mechanism to be proposed as supported by computations.
Braddock D, Lancaster B, Tighe C, et al., 2023, Surmounting byproduct inhibition in an intermolecular catalytic asymmetric alkene bromoesterification reaction as revealed by kinetic profiling, Journal of Organic Chemistry, Vol: 88, Pages: 8904-8914, ISSN: 0022-3263
Kinetic profiling has shown that a (DHQD)2PHAL catalysed intermolecular asymmetric alkene bromoesterification reaction is inhibited by primary amides, imides, hydantoins and secondary cyclic amides, which are by-products of common stoichiometric bromenium ion sources. Two approaches to resolving the inhibition are presented enabling the (DHQD)2PHAL loading to be dropped from 10 to 1 mol% while maintaining high bromoester conversions over short reaction times. Iterative post-reaction recrystallisations enabled a homochiral bromonaphthoate ester to be synthesised using only 1 mol% (DHQD)2PHAL.
Ciccarelli D, Christopher Braddock D, Surman AJ, et al., 2023, Enhanced selectivity for acidic contaminants in drinking water: From suspect screening to toxicity prediction, Journal of Hazardous Materials, Vol: 448, Pages: 1-12, ISSN: 0304-3894
A novel analytical workflow for suspect screening of organic acidic contaminants in drinking water is presented, featuring selective extraction by silica-based strong anion-exchange solid-phase extraction, mixed-mode liquid chromatography-high resolution accurate mass spectrometry (LC-HRMS), peak detection, feature reduction and compound identification. The novel use of an ammonium bicarbonate-based elution solvent extended strong anion-exchange solid-phase extraction applicability to LC-HRMS of strong acids. This approach performed with consistently higher recovery and repeatability (88 ± 7 % at 500 ng L-1), improved selectivity and lower matrix interference (mean = 12 %) over a generic mixed-mode weak anion exchange SPE method. In addition, a novel filter for reducing full-scan features from fulvic and humic acids was successfully introduced, reducing workload and potential for false positives. The workflow was then applied to 10 London municipal drinking water samples, revealing the presence of 22 confirmed and 37 tentatively identified substances. Several poorly investigated and potentially harmful compounds were found which included halogenated hydroxy-cyclopentene-diones and dibromomethanesulfonic acid. Some of these compounds have been reported as mutagenic in test systems and thus their presence here requires further investigation. Overall, this approach demonstrated that employing selective extraction improved detection and helped shortlist suspects and potentially toxic chemical contaminants with higher confidence.
McCarthy S, Desaunay O, Lee Wei Jie A, et al., 2022, Homogeneous gold catalysis using complexes recovered from waste electronic equipment, ACS Sustainable Chemistry and Engineering, Vol: 10, Pages: 15726-15734, ISSN: 2168-0485
Despite the greater awareness of elemental sustainability and the benefits of the circular economy concept, much waste electrical and electronic equipment (WEEE) is still destined for landfill. Effective methods for valorizing this waste within our society are therefore imperative. In this contribution, two gold(III) complexes obtained as recovery products from WEEE and their anion metathesis products were investigated as homogenous catalysts. These four recovery products were successfully applied as catalysts for the cyclization of propargylic amides and the condensation of acetylacetone with o-iodoaniline. Impressive activity was also observed in the gold-catalyzed reaction between electron-rich arenes (2-methylfuran, 1,3-dimethoxybenzene, and azulene) and α,β-unsaturated carbonyl compounds (methyl vinyl ketone and cyclohexenone). These recovered compounds were also shown to be effective catalysts for the oxidative cross-coupling reaction of aryl silanes and arenes. When employed as Lewis acid catalysts for carbonyl-containing substrates, the WEEE-derived gold complexes could also be recovered at the end of the reaction and reused without loss in catalytic activity, enhancing still further the sustainability of the process. This is the first direct application in homogeneous catalysis of gold recovery products sourced from e-waste.
Braddock D, Duran-Corbera A, Nilforoushan M, et al., 2022, (±)-Polysiphenol and other Analogues via Symmetrical Intermolecular Dimerizations: a Synthetic, Spectroscopic, Structural and Computational Study, Journal of Natural Products, Vol: 85, Pages: 2650-2655, ISSN: 0163-3864
We report an improved total synthesis of 4,5-dibromo-9,10-dihydrophenanthrene-2,3,6,7-tetraol, (±)-polysiphenol, via intermolecular McMurray dimerization of 5-bromovanillin and subsequent intramolecular oxidative coupling as the key steps. The synthetic route is applicable to 4,5-dichloro- and 4,5-difluoro-halologues (as well as a 4,5-dialkyl-analogue). Distinctive AA′BB′ multiplets in their 1H NMR spectra for the dimethylene bridges of the dibromo and dichloro compounds reveal them to be room-temperature stable atropisomers, while for the difluoro compound they present as a singlet. X-ray crystal structure determinations of their tetramethylated synthetic precursors show atropisomeric twist angles of 48°, 46°, and 32°, respectively, with the former representing the largest yet observed in any 4,5-disubstituted-9,10-dihydrophenanthrene. DFT computational studies reveal an unprecedented two-stage atropisomeric interconversion process involving time-independent asynchronous rotations of the dimethylene bridge and the biaryl axis for halologues containing chlorine or bromine, but a more synchronous rotation for the difluoro analogue.
Braddock D, Limpaitoon N, Oliwa K, et al., 2022, A stereoselective hydride transfer reaction with contributions from attractive dispersion force control, Chemical Communications, Vol: 58, Pages: 4981-4984, ISSN: 1359-7345
The experimentally determined stereochemical outcome of an unprecedented hydride transfer from a lithium alkoxide to an aldehyde is reported, as deconvoluted by the combined use of a single enantiomer alkoxide in conjunction with a deuterium label. The stereoselective outcome is consistent with a computationally predicted transition state model stabilised by contributions from attractive dispersion forces.
Braddock D, Davies J, Lickiss P, 2022, Methyltrimethoxysilane (MTM) as a reagent for direct amidation of carboxylic acids, Organic Letters, Vol: 24, Pages: 1175-1179, ISSN: 1523-7052
Methyltrimethoxysilane [MTM, CH3Si(OMe)3] has been demonstrated to be an effective, inexpensive, and safe reagent for the direct amidation of carboxylic acids with amines. Two simple workup procedures that provide the pure amide product without the need for further purification have been developed. The first employs an aqueous base-mediated annihilation of MTM. The second involves simple product crystallization from the reaction mixture providing a low process mass intensity direct amidation protocol.
McCarthy S, Braddock D, Wilton-Ely J, 2021, Strategies for sustainable palladium catalysis, Coordination Chemistry Reviews, Vol: 442, Pages: 1-26, ISSN: 0010-8545
Palladium is established both as an indispensable metal in modern synthetic chemistry and as a key component in catalytic converters and electronic equipment. The unrelenting demand for this metal increases both the financial and environmental cost, through mining, of this metal, rendering consumption unsustainable in its current form. This review provides a critical survey of the main approaches being pursued to address this issue, including low-loading catalysis, recyclable catalysts and the use of palladium recovered from secondary sources. The literature discussed herein reveals that catalysts that operate at low loadings are an attractive, sustainable option for many transformations, even when compared to catalyst systems that can be reused multiple times. Both low-loading and reusable catalysts depend on a finite natural supply of palladium, making the development of catalysts based on metal recovered from end-of-life materials (urban mining) a promising field of research. The way in which low-loading is achieved in different catalyst designs influences the choice of reaction temperature and solvent, which has additional environmental implications. Such factors are discussed for a wide range of systems alongside reaction and substrate scope, supported by extensive supplementary information. The survey aims to provide an insight into the relative merits of the approaches being explored and how the field of palladiumbased catalysis might progress towards more sustainable use of this critical metal.
McCarthy S, Lee Wei Jie A, Braddock D, et al., 2021, From waste to green applications: the use of recovered gold and palladium in catalysis, Molecules, Vol: 26, ISSN: 1420-3049
The direct use in catalysis of precious metal recovery products from industrial and consumer waste is a very promising recent area of investigation. It represents a more sustainable, environmentally benign, and profitable way of managing the low abundance of precious metals, as well as encouraging new ways of exploiting their catalytic properties. This review demonstrates the feasibility and sustainability of this innovative approach, inspired by circular economy models, and aims to stimulate further research and industrial processes based on the valorisation of secondary resources of these raw materials. The overview of the use of recovered gold and palladium in catalytic processes will be complemented by critical appraisal of the recovery and reuse approaches that have been proposed.
Davies J, Braddock D, Lickiss P, 2021, Silicon compounds as stoichiometric coupling reagents for direct amidation, Organic and Biomolecular Chemistry, Vol: 19, Pages: 6746-6760, ISSN: 1477-0520
Despite being one of the most frequently carried out chemical reactions in industry, there is currently no amidation protocol that is regarded as safe, high yielding, environmentally friendly and inexpensive. The direct amidation of a carboxylic acid with an amine is viewed as an inherently good solution for developing such a protocol. Since the 1960s, there has been a gradual development in the use of silicon reagents for direct amidation. This review covers the methods published to April 2021 for silicon reagent mediated direct amidation of a carboxylic acid with an amine. This review also covers the use of polymeric SiO2 to promote direct amidation.
Bahou K, Braddock D, Meyer A, et al., 2020, Relay cross metathesis for the iterative construction of terpenoids and synthesis of a diterpene benzoate macrolide of biogenetic relevance to the bromophycolides, Organic Letters, Vol: 22, Pages: 3176-3179, ISSN: 1523-7052
We report a relay cross metathesis (ReXM) reaction for the construction of terpenoids in an iterative protocol. The protocol features the cross metathesis of a relay-actuated Δ6,7-functionalized C10-monoterpenoid alcohol with C10-monoterpenoid citral to form a C15-sesquiterpene. Subsequent functional group manipulation allows for the method to be repeated in an iterative fashion. The method is used for the synthesis of a diterpene-benzoate macrolide of biogenetic relevance to the bromophycolide family of natural products.
Bahou K, Braddock D, Meyer A, et al., 2020, A relay strategy actuates pre-existing trisubstituted olefins in monoterpenoids for cross metathesis with trisubstituted alkenes, The Journal of Organic Chemistry, Vol: 85, Pages: 4906-4917, ISSN: 0022-3263
A retrosynthetic disconnection-reconnection analysis of epoxypolyenes – substrates that can undergo cyclization to podocarpane-type tricycles – reveals relay-actuated 6,7-functionalized monoterpenoid alcohols for ruthenium benzylidene catalyzed olefin cross metathesis with homoprenyl benzenes. Successful implementation of this approach provided several epoxypolyenes as expected (E:Z, ca. 2-3:1). The method is further generalized for the cross metathesis of pre-existing trisubstituted olefins in other relay-actuated 6,7-functionalized monoterpenoid alcohols with various other trisubstituted alkenes to form new trisubstituted olefins. Epoxypolyene cyclization of an enantiomerically pure, but geometrically impure, epoxypolyene substrate provides an enantiomerically pure, trans-fused, podocarpane-type tricycle (from the E-geometrical isomer).
Bahou K, Braddock DC, Meyer AG, et al., 2019, A Relay Strategy Actuates Pre-Existing Trisubstituted Olefins in Monoterpenoids to Form New Trisubstituted Olefins by Cross Metathesis
<jats:p><jats:bold><jats:underline>Abstract:</jats:underline></jats:bold> A retrosynthetic disconnection-reconnection analysis of epoxypolyenes – substrates that can undergo cyclization to podocarpane-type tricycles – reveals relay-actuated Δ<jats:sup>6,7</jats:sup>-functionalized monoterpenoid alcohols for ruthenium benzylidene catalyzed olefin cross metathesis with homoprenyl benzenes. Successful implementation of this approach provided several epoxypolyenes as expected (<jats:italic>E</jats:italic>:<jats:italic>Z</jats:italic>, ca. 2-3:1). The method is further generalized for the cross metathesis of pre-existing trisubstituted olefins in other relay-actuated Δ<jats:sup>6,7</jats:sup>-functionalized monoterpenoid alcohols with various other trisubstituted alkenes to form new trisubstituted olefins. Epoxypolyene cyclization of an enantiomerically pure, but geometrically impure, epoxypolyene substrate provides an enantiomerically pure, trans-fused, podocarpane-type tricycle (from the <jats:italic>E</jats:italic>-geometrical isomer).</jats:p><jats:p />
Bahou K, Braddock DC, Meyer AG, et al., 2019, A Relay Strategy Actuates Pre-Existing Trisubstituted Olefins in Monoterpenoids to Form New Trisubstituted Olefins by Cross Metathesis
<jats:p><b><u>Abstract:</u></b> A retrosynthetic disconnection-reconnection analysis of epoxypolyenes – substrates that can undergo cyclization to podocarpane-type tricycles – reveals relay-actuated Δ<sup>6,7</sup>-functionalized monoterpenoid alcohols for ruthenium benzylidene catalyzed olefin cross metathesis with homoprenyl benzenes. Successful implementation of this approach provided several epoxypolyenes as expected (<i>E</i>:<i>Z</i>, ca. 2-3:1). The method is further generalized for the cross metathesis of pre-existing trisubstituted olefins in other relay-actuated Δ<sup>6,7</sup>-functionalized monoterpenoid alcohols with various other trisubstituted alkenes to form new trisubstituted olefins. Epoxypolyene cyclization of an enantiomerically pure, but geometrically impure, epoxypolyene substrate provides an enantiomerically pure, trans-fused, podocarpane-type tricycle (from the <i>E</i>-geometrical isomer).<br></jats:p>
Bahou K, Braddock DC, Meyer AG, et al., 2019, Relay Cross Metathesis for the Iterative Ascent of the Terpenoids
<jats:p>We report the design and implementation of a relay crossmetathesis (ReXM) reaction for the ascent of the terpenoids in an iterative protocol. The method features the reaction of naturally occurring terpenoid building blocks – with preexisting trisubstituted olefins – which combine to construct a new trisubstituted olefin resulting in a five-carbon unit homologation. Subsequent functional group manipulation allows for the method to be repeated in aniterative fashion. The method is used for the synthesis of a diterpenebenzoate macrolide of biogenetic relevance to the bromophycolide family of natural products.</jats:p>
Bahou K, Braddock DC, Meyer AG, et al., 2019, Relay Cross Metathesis for the Ascent of the Terpenoids
<jats:p>We report the design and implementation of a relay cross metathesis (ReXM) reaction for the ascent of the terpenoids in an iterative protocol using naturally occurring terpenoid building blocks. The method is used for the synthesis of a diterpene-benzoate macrolide of biogenetic relevance to the bromophycolide family of natural products.</jats:p>
Lo Q, Sale D, Braddock D, et al., 2019, New insights into the reaction capabilities of ionic organic bases in cu-catalysed amination, European Journal of Organic Chemistry, Vol: 2019, Pages: 1944-1951, ISSN: 1099-0690
The application of ionic organic bases in the copper‐catalyzed amination reaction (Ullmann reaction) has been studied at room temperature, with sub‐mol‐% catalyst loadings, and with more challenging amines at elevated temperatures. The cation present in the base has been shown to have little effect on the reaction at standard catalyst and ancillary ligand loadings, whereas the choice of anion is crucial for good reactivity. A substrate scope carried out at room temperature with the best performing bases, TBAM and TBPM, showed both bases to be highly effective under these mild reaction conditions. Moreover, under sub‐mol % catalyst loadings and room temperature conditions, TBPM gave good to excellent yields for a number of different amines and functionalized aryl iodides (14 examples). However, reactions involving more challenging amines gave little or no yield. By using more forceful conditions (120 °C) moderate to excellent yields of cross‐coupled products containing more challenging amines was achievable using TBPM and to a lesser extent with TBAM. As part of this work a study on the stability of the organic bases at 120 °C was undertaken. TBAM is shown to decompose to give nBu3N and mono‐butylmalonate at higher temperatures, and this can be correlated to a decrease in performance in the coupling reaction. The phosphonium cations in TBPM did not undergo analogous reactivity but were shown instead to experience some degree of deprotonation at the α‐CH2 to generate phosphonium ylides. This however did not lead to a significantly degradation in the activity of the TBPM in the cross‐coupling reaction.
Braddock DC, Lickiss PD, Rowley BC, et al., 2018, Tetramethyl Orthosilicate (TMOS) as a Reagent for Direct Amidation of Carboxylic Acids, ORGANIC LETTERS, Vol: 20, Pages: 950-953, ISSN: 1523-7060
Lo QA, Sale D, Braddock DC, et al., 2018, Mechanistic and Performance Studies on the Ligand-Promoted Ullmann Amination Reaction, ACS CATALYSIS, Vol: 8, Pages: 101-109, ISSN: 2155-5435
Bahou KA, Braddock DC, Meyer AG, et al., 2017, Kinetic Benchmarking Reveals the Competence of Prenyl Groups in Ring-Closing Metathesis, ORGANIC LETTERS, Vol: 19, Pages: 5332-5335, ISSN: 1523-7060
Clarke J, Bonney KJ, Yaqoob M, 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: 0022-3263
The total syntheses of 12-epoxyobtusallene IV, 12-epoxyobtusallene II, obtusallene X, marilzabicycloallene C, and marilzabicycloallene D as halogenated C15-acetogenin 12-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 synthesized 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 and 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 modeling 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 12-membered bicyclic ether bromoallene was synthesized 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.
Sung S, Sale D, Braddock DC, et al., 2016, Mechanistic Studies on the Copper-Catalyzed N-Arylation of Alkylamines Promoted by Organic Soluble Ionic Bases, ACS CATALYSIS, Vol: 6, Pages: 3965-3974, ISSN: 2155-5435
Campbell J, Burgal JDS, Szekely G, et al., 2016, Hybrid polymer/MOF membranes for Organic Solvent Nanofiltration (OSN): Chemical modification and the quest for perfection, Journal of Membrane Science, Vol: 503, Pages: 166-176, ISSN: 0376-7388
One of the main challenges in the field of Organic Solvent Nanofiltration (OSN) is to improve the selectivity of membranes, allowing the separation of closely related solutes. This objective might be achieved by constructing membranes with uniform porous structures. Hybrid Polymer/Metal Organic Framework (MOF) membranes were prepared by in-situ growth (ISG) of HKUST-1 within the pores of polyimide membranes. To improve the performances of ISG membranes, chemical modification was performed. Aryl carboxylic acid moieties were introduced to polyimide P84 ultrafiltration membranes allowing coordination of the HKUST-1 directly on to the polymer. Chemically modified ISG membranes outperformed non-modified ISG membranes in both solute retentions and permeance. Retentions of polystyrene solute in acetone were used to calculate theoretical pore size distributions for each of the membranes tested. It was found that the chemically modified ISG membrane had he narrowest calculated pore size distribution.
Sung S, Braddock DC, Armstrong A, et al., 2015, Synthesis, Characterisation and Reactivity of Copper(I) Amide Complexes and Studies on Their Role in the Modified Ullmann Amination Reaction, CHEMISTRY-A EUROPEAN JOURNAL, Vol: 21, Pages: 7179-7192, ISSN: 0947-6539
Campbell J, Davies RP, Braddock DC, et al., 2015, Improving the permeance of hybrid polymer/metal-organic framework (MOF) membranes for organic solvent nanofiltration (OSN) - development of MOF thin films via interfacial synthesis, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 3, Pages: 9668-9674, ISSN: 2050-7488
Campbell J, Szekely G, Davies RP, et al., 2014, Fabrication of hybrid polymer/metal organic framework membranes: mixed matrix membranes versus in situ growth, Journal of Materials Chemistry A, Vol: 2, Pages: 9260-9271, ISSN: 2050-7488
Hybrid polymer/metal organic framework (MOF) membranes have been prepared using either a mixed matrix membrane (MMM) or in situ growth (ISG) approach and were evaluated for application in organic solvent nanofiltration (OSN). MMMs were produced by dispersing pre-formed particles of the MOF HKUST-1 in polyimide P84 dope solutions. MMMs demonstrated both (i) higher rejections of styrene oligomers and (ii) lower flux decline than the polymeric control membranes. Furthermore, an alternative hybrid membrane fabrication methodology – in situ growth (ISG) of HKUST-1 in integrally skinned asymmetric polymer membrane supports – has been successfully demonstrated. Ultrafiltration support membranes were submerged in HKUST-1 precursor solutions in order to promote the growth of MOF within the porous structure of the polymer membranes. The presence of HKUST-1 in the membranes was proven with X-ray powder diffraction (XRPD). Energy-dispersive X-ray spectroscopy (EDX) was used to reveal the distribution of HKUST-1 throughout the ISG membranes, and was found to be even across the surface and throughout the cross-section. The ISG membranes also had higher solute rejections and lower flux decline than the MMMs.
Kim M-S, Buisson LA, Heathcote DA, et al., 2014, Approaches to design non-covalent inhibitors for human granzyme B (hGrB), ORGANIC & BIOMOLECULAR CHEMISTRY, Vol: 12, Pages: 8952-8965, ISSN: 1477-0520
Braddock DC, Gao AX, White AJP, et al., 2014, Studies towards the synthesis of halomon: asymmetric hexafunctionalisation of myrcene, CHEMICAL COMMUNICATIONS, Vol: 50, Pages: 13725-13728, ISSN: 1359-7345
Braddock DC, Sbircea D-T, 2014, Proof-of-principle direct double cyclisation of a linear C-15-precursor to a dibrominated bicyclic medium-ring ether relevant to Laurencia species, CHEMICAL COMMUNICATIONS, Vol: 50, Pages: 12691-12693, ISSN: 1359-7345
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