The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Sophie M. Guillaume - One of the best experts on this subject based on the ideXlab platform.
-
α ω epoxide oxetane and dithiocarbonate telechelic copolyolefins access by ring opening metathesis cross metathesis polymerization romp cm of cycloolefins in the presence of functional symmetric chain transfer agents
Polymers, 2018Co-Authors: E. Vanbiervliet, S. Fouquay, G. Michaud, F. Simon, Jeanfrancois Carpentier, Sophie M. GuillaumeAbstract:Epoxide- and oxetane-α,ω-telechelic (co)polyolefins have been successfully synthesized by the tandem ring-opening metathesis polymerization (ROMP)/cross-metathesis (CM) of cyclic olefins using Grubbs' second-generation catalyst (G2) in the presence of a bifunctional symmetric alkene epoxide- or oxetane-functionalized chain-transfer agent (CTA). From cyclooctene (COE), trans,trans,cis-1,5,9-cyclododecatriene (CDT), norbornene (NB), and methyl 5-norbornene-2-carboxylate (NBCOOMe), with bis(oxiran-2-ylmethyl) maleate (CTA 1), bis(oxetane-2-ylmethyl) maleate (CTA 2), or bis(oxetane-2-ylmethyl) (E)-hex-3-enedioate (CTA 3), well-defined α,ω-di(epoxide or oxetane) telechelic PCOEs, P(COE-co-NB or -NBCOOMe)s, and P(NB-co-CDT)s were isolated under mild operating conditions (40 or 60 °C, 24 h). The oxetane CTA 3 and the epoxide CTA 1 were revealed to be significantly more efficient in the CM step than CTA 2, which apparently inhibits the reaction. Quantitative dithiocarbonatation (CS₂/LiBr, 40 °C, THF) of an α,ω-di(epoxide) telechelic P(NB-co-CDT) afforded a convenient approach to the analogous α,ω-bis(dithiocarbonate) telechelic P(NB-co-CDT). The nature of the end-capping function of the epoxide/oxetane/dithiocarbonate telechelic P(NB-co-CDT)s did not impact their thermal signature, as measured by DSC. These copolymers also displayed a low viscosity liquid-like behavior and a shear thinning rheological behavior.
Mark W Peczuh - One of the best experts on this subject based on the ideXlab platform.
-
a practical and scalable synthesis of carbohydrate based oxepines
Organic and Biomolecular Chemistry, 2016Co-Authors: Raghu Vannam, Mark W PeczuhAbstract:An efficient, seven-step synthesis of carbohydrate based oxepines is reported using per-O-acetyl septanoses as key intermediates. The scope of the synthesis was evaluated by varying both the pyranose starting materials and protecting groups incorporated into the oxepine products. The practicality of the method make it amenable to scale up as demonstrated by the gram-scale synthesis of the D-glucose derived oxepine.
-
stereoselectivity in the epoxidation of carbohydrate based oxepines
Journal of Organic Chemistry, 2008Co-Authors: Shankar D Markad, Nicole L Snyder, Bikash Surana, Martha D Morton, Christopher M Hadad, Mark W PeczuhAbstract:The facial selectivity in the DMDO epoxidation of carbohydrate-based oxepines derived from glucose, galactose, and mannose has been determined by product analysis and density functional theory (DFT, B3LYP/6-31+G**//B3LYP/6-31G*) calculations. Oxepines 3 and 4, derived from d-galactose and d-mannose, largely favor α- over β-epoxidation. The results reported here, along with selectivities in the DMDO-mediated epoxidation of d-xylose-based oxepine 1 and d-glucose-based oxepines 2 and 5 reported earlier, support a model in which electronic effects, guided by the stereochemistry of the oxygens on the oxepine ring, largely determine the stereoselectivity of epoxidation. Other contributing factors included conformational issues in the oxepine’s transition state relative to the reactant, the asynchronicity in bond formation of the epoxide, and the overall steric bulk on the α- and β-faces of the oxepine. Considered together, these factors should generally predict facial selectivity in the DMDO-epoxidation of cycl...
Visuvanathar Sridharan - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of oxetane/azetidine containing spirocycles
Tetrahedron Letters, 2019Co-Authors: Rosalie Hamill, Christopher M Pask, Benjamin Jones, Visuvanathar SridharanAbstract:Oxetane-benzopyran spirocycles were synthesised via a palladium catalysed cyclisation-cross coupling cascade reaction whilst oxetane/azetidine-pyrrolidino isoindolone spirocycles were synthesised via a silver catalysed 1,3-dipolar cycloaddition reaction followed by a palladium catalysed carbonylation-amination process.
-
synthesis of oxetane azetidine containing spirocycles via the 1 3 dipolar cycloaddition reaction
Tetrahedron Letters, 2016Co-Authors: Benjamin Jones, Mitchell Proud, Visuvanathar SridharanAbstract:Abstract Silver catalyzed 1,3-dipolar cycloaddition reactions between methyl 2-(oxetane/azetidine-3 ylidene)acetate as dipolarophiles and imines derived from α-amino acid methyl esters, 2-aminomethyl pyridine, and 2-aminomethyl pyrazine afforded oxetane/azetidine containing spirocycles in 40–77% yield. The use of 3-oxetanone used as the carbonyl compound thermal 1,3-dipolar cycloaddition reactions with secondary α-amino acids or methyl esters resulted in oxetane spirocycles in 62–90% yield.
Donald J. Darensbourg - One of the best experts on this subject based on the ideXlab platform.
-
an investigation of the pathways for oxygen sulfur scramblings during the copolymerization of carbon disulfide and oxetane
Macromolecules, 2015Co-Authors: Ming Luo, Xinghong Zhang, Donald J. DarensbourgAbstract:The catalytic coupling of oxetane, the symmetric isomer of propylene oxide, with carbon disulfide has been investigated utilizing (salen)CrCl in the presence of various onium salts. Oxygen and sulfur atom exchange was observed in both the polymeric and cyclic carbonate products. The coupling of oxetane and CS2 was selective for copolymer formation over a wide range of reaction conditions. Five different polymer linkages and two cyclic products were determined by 1H and 13C NMR spectroscopy, and these results were consistent with in situ infrared spectroscopic monitoring of the process. The major cyclic product produced in the coupling process was trimethylene trithiocarbonate, which was isolated and characterized by single crystal X-ray crystallography. Upon increasing the CS2/oxetane feed ratio, a decrease in the O/S scrambling occurred. The reaction temperature had the most significant effect on the O/S exchange process, increasing exchange with increasing temperature. The presence of the onium salt ini...
-
aliphatic polycarbonates produced from the coupling of carbon dioxide and oxetanes and their depolymerization via cyclic carbonate formation
Macromolecules, 2011Co-Authors: Donald J. Darensbourg, Adriana I MoncadaAbstract:The (salen)CrCl/onium salt catalyzed coupling reactions of several oxetane derivatives and carbon dioxide are reported. The oxetanes investigated contain substituents in the 3-position covering a range of steric requirements. The oxetanes examined include, 3,3-dimethyloxetane, 3-methoxymethyl-3-methyloxetane, and 3-benzyloxymethyl-3-methyloxetane. The rates of reaction of these oxetanes with CO2 were found to be significantly slower than the corresponding process with the parent oxetane monomer. Furthermore, in these instances the formation of copolymer was found to proceed via the preformed cycloaddition product, i.e., the six-membered cyclic carbonate, to a greater extent and increasing with the steric bulk of the substituents on oxetane. For these sterically more hindered oxetanes, the CO2 coupling reaction carried out in toluene at 110 °C reached an equilibrium product distribution of copolymer to cyclic carbonate which increased in cyclic carbonate product with increasing steric requirements of the o...
-
salen co ii n bu4nx catalysts for the coupling of co2 and oxetane selectivity for cyclic carbonate formation in the production of poly trimethylene carbonate
Macromolecules, 2009Co-Authors: Donald J. Darensbourg, Adriana I MoncadaAbstract:The (salen)Co(II) complex ((1R,2R)-(−)-1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)cobalt(II)) in the presence of an anion initiator, e.g. bromide, has been shown to be a very effective catalytic system for the coupling of oxetane and carbon dioxide, to provide the corresponding polycarbonate with minimal amount of ether linkages. The mechanism of the coupling of oxetane and carbon dioxide has been studied by in situ infrared spectroscopy, where the first formed product is trimethylene carbonate (TMC). TMC is formed by a backbiting mechanism following ring-opening of oxetane by the anion initiator, subsequent to CO2 insertion into the cobalt−oxygen bond. The formation of the copolymer is shown to proceed mostly by way of the anionic ring-opening polymerization of preformed trimethylene carbonate in the presence of an anion in solution. Anions that are good leaving groups, i.e., bromide and iodide, are most effective at affording copolymer via this route. In the presence of greater than 2...
-
mechanistic studies of the copolymerization reaction of oxetane and carbon dioxide to provide aliphatic polycarbonates catalyzed by salen crx complexes
Journal of the American Chemical Society, 2008Co-Authors: Donald J. Darensbourg, Adriana I Moncada, Wonsook Choi, Joseph H ReibenspiesAbstract:Chromium salen derivatives in the presence of anionic initiators have been shown to be very effective catalytic systems for the selective coupling of oxetane and carbon dioxide to provide the corresponding polycarbonate with a minimal amount of ether linkages. Optimization of the chromium(III) system was achieved utilizing a salen ligand with tert-butyl groups in the 3,5-positions of the phenolate rings and a cyclohexylene backbone for the diimine along with an azide ion initiator. The mechanism for the coupling reaction of oxetane and carbon dioxide has been studied. Based on binding studies done by infrared spectroscopy, X-ray crystallography, kinetic data, end group analysis done by 1H NMR, and infrared spectroscopy, a mechanism of the copolymerization reaction is proposed. The formation of the copolymer is shown to proceed in part by way of the intermediacy of trimethylene carbonate, which was observed as a minor product of the coupling reaction, and by the direct enchainment of oxetane and CO2. The p...
Adriana I Moncada - One of the best experts on this subject based on the ideXlab platform.
-
aliphatic polycarbonates produced from the coupling of carbon dioxide and oxetanes and their depolymerization via cyclic carbonate formation
Macromolecules, 2011Co-Authors: Donald J. Darensbourg, Adriana I MoncadaAbstract:The (salen)CrCl/onium salt catalyzed coupling reactions of several oxetane derivatives and carbon dioxide are reported. The oxetanes investigated contain substituents in the 3-position covering a range of steric requirements. The oxetanes examined include, 3,3-dimethyloxetane, 3-methoxymethyl-3-methyloxetane, and 3-benzyloxymethyl-3-methyloxetane. The rates of reaction of these oxetanes with CO2 were found to be significantly slower than the corresponding process with the parent oxetane monomer. Furthermore, in these instances the formation of copolymer was found to proceed via the preformed cycloaddition product, i.e., the six-membered cyclic carbonate, to a greater extent and increasing with the steric bulk of the substituents on oxetane. For these sterically more hindered oxetanes, the CO2 coupling reaction carried out in toluene at 110 °C reached an equilibrium product distribution of copolymer to cyclic carbonate which increased in cyclic carbonate product with increasing steric requirements of the o...
-
salen co ii n bu4nx catalysts for the coupling of co2 and oxetane selectivity for cyclic carbonate formation in the production of poly trimethylene carbonate
Macromolecules, 2009Co-Authors: Donald J. Darensbourg, Adriana I MoncadaAbstract:The (salen)Co(II) complex ((1R,2R)-(−)-1,2-cyclohexanediamino-N,N′-bis(3,5-di-tert-butylsalicylidene)cobalt(II)) in the presence of an anion initiator, e.g. bromide, has been shown to be a very effective catalytic system for the coupling of oxetane and carbon dioxide, to provide the corresponding polycarbonate with minimal amount of ether linkages. The mechanism of the coupling of oxetane and carbon dioxide has been studied by in situ infrared spectroscopy, where the first formed product is trimethylene carbonate (TMC). TMC is formed by a backbiting mechanism following ring-opening of oxetane by the anion initiator, subsequent to CO2 insertion into the cobalt−oxygen bond. The formation of the copolymer is shown to proceed mostly by way of the anionic ring-opening polymerization of preformed trimethylene carbonate in the presence of an anion in solution. Anions that are good leaving groups, i.e., bromide and iodide, are most effective at affording copolymer via this route. In the presence of greater than 2...
-
mechanistic studies of the copolymerization reaction of oxetane and carbon dioxide to provide aliphatic polycarbonates catalyzed by salen crx complexes
Journal of the American Chemical Society, 2008Co-Authors: Donald J. Darensbourg, Adriana I Moncada, Wonsook Choi, Joseph H ReibenspiesAbstract:Chromium salen derivatives in the presence of anionic initiators have been shown to be very effective catalytic systems for the selective coupling of oxetane and carbon dioxide to provide the corresponding polycarbonate with a minimal amount of ether linkages. Optimization of the chromium(III) system was achieved utilizing a salen ligand with tert-butyl groups in the 3,5-positions of the phenolate rings and a cyclohexylene backbone for the diimine along with an azide ion initiator. The mechanism for the coupling reaction of oxetane and carbon dioxide has been studied. Based on binding studies done by infrared spectroscopy, X-ray crystallography, kinetic data, end group analysis done by 1H NMR, and infrared spectroscopy, a mechanism of the copolymerization reaction is proposed. The formation of the copolymer is shown to proceed in part by way of the intermediacy of trimethylene carbonate, which was observed as a minor product of the coupling reaction, and by the direct enchainment of oxetane and CO2. The p...
