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276 results on '"Ashfeld, Brandon L."'

95. Hierarchically porous materials via assembly of nitrogen-rich polymer nanoparticles for efficient and selective CO2 capture.

Author

Lee, Doyun, Zhang, Chengyi, Wei, Chuan, Ashfeld, Brandon L., and Gao, Haifeng

Abstract

Hierarchically porous materials were developed using a two-step procedure by (1) the stacking of high-nitrogen-content polymer nanoparticles to produce inter-particle mesoporous space and (2) chemical activation to create intra-particle micropores. The materials exhibited efficient CO2 uptake and enhanced CO2/N2 selectivity, which is 40% higher than that of the control material without a hierarchical structure. [ABSTRACT FROM AUTHOR]

Published
2013
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96. Amine-Free Approach toward N-Toluenesulfonyl Amidine Construction: A Phosphite-Mediated Beckmann-Like Coupling of Oximes and p-Toluenesulfonyl Azide.

Author

Fleury, Lauren M., Wilson, Erin E., Vogt, Monika, Fan, Tiffany J., Oliver, Allen G., and Ashfeld, Brandon L.

Subjects
AMIDINES, AZIDES, OXIMES, BECKMANN rearrangement, BIOACTIVE compounds, BIOCHEMISTRY
Abstract

Atom hopping: A chlorophosphite‐mediated Beckmann ligation of oximes and p‐toluenesulfonyl azide gives access to N‐sulfonyl phosphoramidines in good to excellent yields. The reaction proceeds under exceptionally mild conditions and constitutes a bioorthogonal approach toward amidines by avoiding the use of amines and transition‐metal catalysts. dmp‐ol=3,3‐dimethylpropanediol. [ABSTRACT FROM AUTHOR]

Published
2013
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97. Solid-State Covalent Capture of CO2 by Using N-Heterocyclic Carbenes.

Author

Vogt, Monika, Bennett, Joshua E., Huang, Yong, Wu, Chao, Schneider, William F., Brennecke, Joan F., and Ashfeld, Brandon L.

Subjects
CARBON sequestration, CARBON dioxide adsorption, SOLID state chemistry, CARBENES, HETEROCYCLIC compounds, GRAVIMETRIC analysis
Abstract

Capture me! The first report of an N‐heterocyclic carbene (NHC) as a solid‐state carbon capture reagent is presented. Experimental and theoretical measurements demonstrate the ability of the NHC to react rapidly and stoichiometrically with CO2 at low partial pressures (see scheme). [ABSTRACT FROM AUTHOR]

Published
2013
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99. Features and Applications of [Rh(CO)2Cl]2-Catalyzed Alkylations of Unsymmetrical Allylic Substrates.

Author

Ashfeld, Brandon L., Miller, Kenneth A., Smith, Anna J., Tran, Kristy, and Martin, Stephen F.

Subjects
*ALKYLATION, *CHEMICAL reactions, *CARBONATES, *RING formation (Chemistry), *STEREOCHEMISTRY
Abstract

A novel regio- and stereoselective [Rh(CO)2Cl]2-catalyzed allylic alkylation of unsymmetrical allylic carbonates was discovered. The regioselectivity of the reaction favors product ratios in which substitution occurs at the carbon bearing the leaving group. When an enantiomerically enriched carbonate (⩾99% ee) was examined, the Rh(I)-catalyzed allylic alkylation proceeded stereoselectively to provide the alkylation product with retention of absolute stereochemistry (98% ee). To establish the scope of the [Rh(CO)2Cl]2-catalyzed allylic alkylation, a variety of carbon and heteroatom nucleophiles were examined and the results described. As an application of the Rh(I)-catalyzed allylic alkylation, a series of novel domino reactions have been developed that couple the unique regio- and stereoselective [Rh(CO)2Cl]2- catalyzed alkylation of allylic trifluoroacetates with an intramolecular Pauson-Khand annulation, a cycloisomerization, or a [5+2] cycloaddition. A unique aspect of the method described is the use of a single catalyst to effect sequential transformations in which the catalytic activity is moderated simply by controlling the reaction temperature. Implementation of such processes provides a rapid and efficient entry to a variety of bicyclic carbon skeletons from simple precursors. [ABSTRACT FROM AUTHOR]

Published
2007
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100. Site specific carboxylation of abnormal anionic N-heterocyclic dicarbenes with CO2.

Author

Vogt, Monika, Wu, Chao, Oliver, Allen G., Meyer, Christopher J., Schneider, William F., and Ashfeld, Brandon L.

Subjects
CARBOXYLATION, HETEROCYCLIC compounds, HETEROCYCLIC chemistry, CARBENES, TRANSITION metal catalysts
Abstract

Herein, we report experimental and computational results for the carboxylation of abnormal anionic N-heterocyclic dicarbenes (NHDCs) with CO2. Under ambient dosing conditions, carbonyl addition occurs selectively at C4 without a second carboxylation event occurring at the C2 carbene center. [ABSTRACT FROM AUTHOR]

Published
2013
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