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  • Journal article
    Lo Q, Sale D, Braddock D, Davies Ret 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.

  • Journal article
    Braddock DC, Lickiss P, Rowley B, Pugh DC, purnomo, Santhakumar G, fussell Set al., 2018,

    Tetramethyl Orthosilicate (TMOS) as a Reagent for Direct Amidation of Carboxylic Acids

    , Organic Letters, Vol: 20, Pages: 950-953, ISSN: 1523-7052

    Tetramethyl orthosilicate (TMOS) is shown to be an effective reagent for direct amidation of aliphatic and aromatic carboxylic acids with amines and anilines. The amide products are obtained in good to quantitative yields in pure form directly after workup without the need for any further purification. A silyl ester as the putative activated intermediate is observed by NMR methods. Amidations on a 1 mol scale are demonstrated with a favorable process mass intensity.

  • Journal article
    Lo QA, Sale D, Braddock DC, Davies RPet al., 2017,

    Mechanistic and Performance Studies on the Ligand Promoted Ullmann Amination Reaction

    , ACS Catalysis, Vol: 8, Pages: 101-109, ISSN: 2155-5435

    Over the last two decades many different auxiliary ligand systems have been utilized in the copper-catalyzed Ullmann amination reaction. However, there has been little consensus on the relative merits of the varied ligands and the exact role they might play in the catalytic process. Accordingly, in this work some of the most commonly employed auxiliary ligands have been evaluated for C–N coupling using reaction progress kinetic analysis (RPKA) methodology. The results reveal not only the relative kinetic competencies of the different auxiliary ligands but also their markedly different influences on catalyst degradation rates. For the model Ullmann reaction between piperidine and iodobenzene using the soluble organic base bis(tetra-n-butylphosphonium) malonate (TBPM) at room temperature, N-methylglycine was shown to give the best performance in terms of high catalytic rate of reaction and comparatively low catalyst deactivation rates. Further experimental and rate data indicate a common catalytic cycle for all auxiliary ligands studied, although additional off-cycle processes are observed for some of the ligands (notably phenanthroline). The ability of the auxiliary ligand, base (malonate dianion), and substrate (amine) to all act competitively as ligands for the copper center is also demonstrated. On the basis of these results an improved protocol for room-temperature copper-catalyzed C–N couplings is presented with 27 different examples reported.

  • Journal article
    Braddock DC, Rzepa HS, Clarke J, Bonney KJ, Yaqoob M, Solanki S, White AJP, Millan Det 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.

  • Journal article
    Braddock DC, Mahtey A, Rzepa HS, White AJPet al., 2016,

    Stable bromoallene oxides

    , Chemical Communications, Vol: 52, Pages: 11219-11222, ISSN: 1364-548X

    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.

  • Journal article
    Sung S, Sale D, Braddock DC, Armstrong A, Brenan C, Davies RPet 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

    Experimental studies on the mechanism of copper-catalyzed amination of aryl halides have been undertaken for the coupling of piperidine with iodobenzene using a Cu(I) catalyst and the organic base tetrabutylphosphonium malonate (TBPM). The use of TBPM led to high reactivity and high conversion rates in the coupling reaction, as well as obviating any mass transfer effects. The often commonly employed O,O-chelating ligand 2-acetylcyclohexanone was surprisingly found to have a negligible effect on the reaction rate, and on the basis of NMR, calorimetric, and kinetic modeling studies, the malonate dianion in TBPM is instead postulated to act as an ancillary ligand in this system. Kinetic profiling using reaction progress kinetic analysis (RPKA) methods show the reaction rate to have a dependence on all of the reaction components in the concentration range studied, with first-order kinetics with respect to [amine], [aryl halide], and [Cu]total. Unexpectedly, negative first-order kinetics in [TBPM] was observed. This negative rate dependence in [TBPM] can be explained by the formation of an off-cycle copper(I) dimalonate species, which is also argued to undergo disproportionation and is thus responsible for catalyst deactivation. The key role of the amine in minimizing catalyst deactivation is also highlighted by the kinetic studies. An examination of the aryl halide activation mechanism using radical probes was undertaken, which is consistent with an oxidative addition pathway. On the basis of these findings, a more detailed mechanistic cycle for the C–N coupling is proposed, including catalyst deactivation pathways.

  • Journal article
    Campbell J, Burgal JDS, Szekely G, Davies RP, Braddock DC, Livingston Aet 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: 1873-3123

    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.

  • Journal article
    Sung S, Braddock DC, Armstrong A, Brennan C, Sale D, White AJP, Davies RPet 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
  • Journal article
    Campbell J, Davies RP, Braddock DC, Livingston AGet 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
  • Journal article
    Kim M-S, Buisson LA, Heathcote DA, Hu H, Braddock DC, Barrett AGM, Ashton-Rickardt PG, Snyder JPet al., 2014,

    Approaches to design non-covalent inhibitors for human granzyme B (hGrB)

    , ORGANIC & BIOMOLECULAR CHEMISTRY, Vol: 12, Pages: 8952-8965, ISSN: 1477-0520

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