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Waldemar Adam - One of the best experts on this subject based on the ideXlab platform.
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nickel catalyzed hydroxylation of 1 3 dicarbonyl compounds by Dimethyldioxirane
ChemInform, 2010Co-Authors: Waldemar Adam, Alexander K SmerzAbstract:Abstract Various 1,3-dicarbonyl compounds were directly hydroxylated by Dimethyldioxirane, a preparative useful extension of this oxidation is the efficient catalysis by Ni(II) salts through chelation. Various 1,3-dicarbonyl compounds were directly hydroxylated by Dimethyldioxirane, a preparative useful extension of this oxidation is the efficient catalysis by Ni(II) salts through chelation. Download full-size image
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relative reactivity of peracids versus dioxiranes dmdo and tfdo in the epoxidation of alkenes a combined experimental and theoretical analysis
Journal of the American Chemical Society, 2003Co-Authors: Robert D. Bach, Waldemar Adam, Olga Dmitrenko, Simon B SchambonyAbstract:Comparative analysis of the calculated gas-phase activation barriers (ΔE⧧) for the epoxidation of ethylene with Dimethyldioxirane (DMDO) and peroxyformic acid (PFA) [15.2 and 16.4 kcal/mol at QCISD...
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a comparative study of the epoxidation of 2 substituted isoflavones by Dimethyldioxirane sodium hypochlorite and alkaline hydrogen peroxide weitz scheffer reaction
Journal of Heterocyclic Chemistry, 2000Co-Authors: Albert Lévai, Waldemar Adam, Tamas Patonay, Andrea Szekely, Erzsebet B Vass, Jozsef JekoAbstract:The comparative epoxidation of 2-substituted isoflavones 9–16 has been conducted by the utilization of three different protocols, viz. epoxidation with isolated Dimethyldioxirane (Method A), with sodium hypochlorite (Method B), and with alkaline hydrogen peroxide (Method C), to afford epoxides 17–24. Best results have been obtained with Method C (Weitz-Scheffer epoxidation). The structures of epoxides have been assigned on the basis of nmr spectral and mass spectral data.
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enantioselective epoxidation of isoflavones by jacobsen s mn iii salen catalysts and Dimethyldioxirane oxygen atom source
ChemInform, 1998Co-Authors: Waldemar Adam, Albert Lévai, Tamas Patonay, Rainer T Fell, K Peters, Andras Simon, Gabor TothAbstract:Abstract The catalytic enantioselective epoxidation of the isoflavones 1a–f has been performed by the Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and Dimethyldioxirane as the oxygen-atom source to afford optically active isoflavone epoxides 2a–f. The absolute configuration of the nonracemic epoxides 2 have been determined by X-ray diffraction analysis. Our present results constitute the first examples of the preparation of optically active isoflavone epoxides.
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determination of the absolute configuration of optically active 2 2 dimethyl 3 4 epoxychromans prepared by the catalytic enantioselective epoxidation with the Dimethyldioxirane jacobsen mn iii salen system
Tetrahedron-asymmetry, 1996Co-Authors: Waldemar Adam, Albert Lévai, Tamas Patonay, Jozsef Jeko, Zsuzsa Majer, Csaba Nemes, Laszlo Parkanyi, Peter SebokAbstract:Abstract Enantioselective epoxidation of 2,2-dimethyl-2 H -chromenes 1a-d by using Mn(III)salen complexes (R,R)- 3 and (S,S)- 3 as catalysts and Dimethyldioxirane (DMD) as oxygen donor afforded optically active 2,2-dimethyl-3,4-epoxychromans 2a-d in good yields and high enantioselectivities (up to 93% e.e.). The absolute configuration of the (3 S ,4 S )-6,7-bis(tosyloxy)-2,2-dimethyl-3,4-epoxychroman (3S,4S)- 2d has been determined by X-ray diffraction. The absolute configurations of the other nonracemic epoxychromans were assigned by circular dichroism (CD) measurements relative to the (3S,4S)- 2d epoxide as reference compound.
Wenhua Zheng - One of the best experts on this subject based on the ideXlab platform.
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chiral phosphoric acid catalyzed highly enantioselective desymmetrization of 2 substituted and 2 2 disubstituted 1 3 diols via oxidative cleavage of benzylidene acetals
ChemInform, 2015Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:This highly enantioselective reaction proceeds through formation of an “ortho ester” intermediate via oxidation of the 1,3-diol benzylidene acetal by Dimethyldioxirane and a subsequent proton transfer catalyzed by chiral phosphoric acids (CPA).
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chiral phosphoric acid catalyzed highly enantioselective desymmetrization of 2 substituted and 2 2 disubstituted 1 3 diols via oxidative cleavage of benzylidene acetals
Journal of the American Chemical Society, 2014Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:A highly enantioselective catalytic protocol for the desymmetrization of a wide variety of 2-substituted and 2,2-disubstituted 1,3-diols is reported. This reaction proceeds through the formation of an “ortho ester” intermediate via oxidation of 1,3-diol benzylidene acetal by Dimethyldioxirane (DMDO) and the subsequent proton transfer catalyzed by chiral phosphoric acid (CPA). The mechanism and origins of enantioselectivity of this reaction are identified using DFT calculations. The oxidation by DMDO is rate-determining, and the phosphoric acid significantly accelerates the proton transfer; the attractive interactions between the benzylidene part of the substrate and the 2,4,6-triisopropyl group of CPA are the key to high enantioselectivity.
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Chiral Phosphoric Acid Catalyzed Highly Enantioselective Desymmetrization of 2‑Substituted and 2,2-Disubstituted 1,3-Diols via Oxidative Cleavage of Benzylidene Acetals
2014Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:A highly enantioselective catalytic protocol for the desymmetrization of a wide variety of 2-substituted and 2,2-disubstituted 1,3-diols is reported. This reaction proceeds through the formation of an “ortho ester” intermediate via oxidation of 1,3-diol benzylidene acetal by Dimethyldioxirane (DMDO) and the subsequent proton transfer catalyzed by chiral phosphoric acid (CPA). The mechanism and origins of enantioselectivity of this reaction are identified using DFT calculations. The oxidation by DMDO is rate-determining, and the phosphoric acid significantly accelerates the proton transfer; the attractive interactions between the benzylidene part of the substrate and the 2,4,6-triisopropyl group of CPA are the key to high enantioselectivity
Shanshui Meng - One of the best experts on this subject based on the ideXlab platform.
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chiral phosphoric acid catalyzed highly enantioselective desymmetrization of 2 substituted and 2 2 disubstituted 1 3 diols via oxidative cleavage of benzylidene acetals
ChemInform, 2015Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:This highly enantioselective reaction proceeds through formation of an “ortho ester” intermediate via oxidation of the 1,3-diol benzylidene acetal by Dimethyldioxirane and a subsequent proton transfer catalyzed by chiral phosphoric acids (CPA).
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chiral phosphoric acid catalyzed highly enantioselective desymmetrization of 2 substituted and 2 2 disubstituted 1 3 diols via oxidative cleavage of benzylidene acetals
Journal of the American Chemical Society, 2014Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:A highly enantioselective catalytic protocol for the desymmetrization of a wide variety of 2-substituted and 2,2-disubstituted 1,3-diols is reported. This reaction proceeds through the formation of an “ortho ester” intermediate via oxidation of 1,3-diol benzylidene acetal by Dimethyldioxirane (DMDO) and the subsequent proton transfer catalyzed by chiral phosphoric acid (CPA). The mechanism and origins of enantioselectivity of this reaction are identified using DFT calculations. The oxidation by DMDO is rate-determining, and the phosphoric acid significantly accelerates the proton transfer; the attractive interactions between the benzylidene part of the substrate and the 2,4,6-triisopropyl group of CPA are the key to high enantioselectivity.
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Chiral Phosphoric Acid Catalyzed Highly Enantioselective Desymmetrization of 2‑Substituted and 2,2-Disubstituted 1,3-Diols via Oxidative Cleavage of Benzylidene Acetals
2014Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:A highly enantioselective catalytic protocol for the desymmetrization of a wide variety of 2-substituted and 2,2-disubstituted 1,3-diols is reported. This reaction proceeds through the formation of an “ortho ester” intermediate via oxidation of 1,3-diol benzylidene acetal by Dimethyldioxirane (DMDO) and the subsequent proton transfer catalyzed by chiral phosphoric acid (CPA). The mechanism and origins of enantioselectivity of this reaction are identified using DFT calculations. The oxidation by DMDO is rate-determining, and the phosphoric acid significantly accelerates the proton transfer; the attractive interactions between the benzylidene part of the substrate and the 2,4,6-triisopropyl group of CPA are the key to high enantioselectivity
Albert Lévai - One of the best experts on this subject based on the ideXlab platform.
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a comparative study of the epoxidation of 2 substituted isoflavones by Dimethyldioxirane sodium hypochlorite and alkaline hydrogen peroxide weitz scheffer reaction
Journal of Heterocyclic Chemistry, 2000Co-Authors: Albert Lévai, Waldemar Adam, Tamas Patonay, Andrea Szekely, Erzsebet B Vass, Jozsef JekoAbstract:The comparative epoxidation of 2-substituted isoflavones 9–16 has been conducted by the utilization of three different protocols, viz. epoxidation with isolated Dimethyldioxirane (Method A), with sodium hypochlorite (Method B), and with alkaline hydrogen peroxide (Method C), to afford epoxides 17–24. Best results have been obtained with Method C (Weitz-Scheffer epoxidation). The structures of epoxides have been assigned on the basis of nmr spectral and mass spectral data.
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enantioselective epoxidation of isoflavones by jacobsen s mn iii salen catalysts and Dimethyldioxirane oxygen atom source
ChemInform, 1998Co-Authors: Waldemar Adam, Albert Lévai, Tamas Patonay, Rainer T Fell, K Peters, Andras Simon, Gabor TothAbstract:Abstract The catalytic enantioselective epoxidation of the isoflavones 1a–f has been performed by the Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and Dimethyldioxirane as the oxygen-atom source to afford optically active isoflavone epoxides 2a–f. The absolute configuration of the nonracemic epoxides 2 have been determined by X-ray diffraction analysis. Our present results constitute the first examples of the preparation of optically active isoflavone epoxides.
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determination of the absolute configuration of optically active 2 2 dimethyl 3 4 epoxychromans prepared by the catalytic enantioselective epoxidation with the Dimethyldioxirane jacobsen mn iii salen system
Tetrahedron-asymmetry, 1996Co-Authors: Waldemar Adam, Albert Lévai, Tamas Patonay, Jozsef Jeko, Zsuzsa Majer, Csaba Nemes, Laszlo Parkanyi, Peter SebokAbstract:Abstract Enantioselective epoxidation of 2,2-dimethyl-2 H -chromenes 1a-d by using Mn(III)salen complexes (R,R)- 3 and (S,S)- 3 as catalysts and Dimethyldioxirane (DMD) as oxygen donor afforded optically active 2,2-dimethyl-3,4-epoxychromans 2a-d in good yields and high enantioselectivities (up to 93% e.e.). The absolute configuration of the (3 S ,4 S )-6,7-bis(tosyloxy)-2,2-dimethyl-3,4-epoxychroman (3S,4S)- 2d has been determined by X-ray diffraction. The absolute configurations of the other nonracemic epoxychromans were assigned by circular dichroism (CD) measurements relative to the (3S,4S)- 2d epoxide as reference compound.
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enantioselective epoxidation of 2 2 dimethyl 2h chromenes by Dimethyldioxirane and jacobsen s mn iii salen catalysts
Tetrahedron Letters, 1995Co-Authors: Waldemar Adam, Albert Lévai, Tamas Patonay, Jozsef Jekő, Csaba Nemes, Peter SebőkAbstract:Enantioselective epoxidation of 2,2-dimethyl-2H-chromenes 1a-d has been performed by the Mn(III)salen complexes (R,R)-3 and (S,S)-3 as catalysts and Dimethyldioxirane (DMD) as oxygen donor. The epoxychromans 2a-d were obtained in good yields and high enantioselectivities (up to 93% e.e.), which constitute the first examples of enantioselective epoxidation by DMD with the Jacobsen catalyst.
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Dimethyldioxirane epoxidation of aurones and isoflavones
Synthesis, 1992Co-Authors: Waldemar Adam, Lazaros P. Hadjiarapoglou, Albert LévaiAbstract:The synthesis of the corresponding epoxides 2 and 4 by epoxidation of aurones (2-benzylidenebenzofuran-3(2H)-ones, 1) and isoflavones (3-aryl-4H-1-benzopyran-4-ones, 3) with Dimethyldioxirane at subambient temperatures is reported. These acid- and base-sensitive epoxides, which have been previously difficult to prepare, were isolated in excellent yields and were completely characterized by spectral and microanalytical data. The now readily available aurone and/or isoflavone oxides may serve as convenient precursors to flavonoid-type natural products
K N Houk - One of the best experts on this subject based on the ideXlab platform.
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Molecular Dynamics of Dimethyldioxirane C–H Oxidation
2016Co-Authors: Zhongyue Yang, K N HoukAbstract:We report molecular dynamics simulations of the reaction of Dimethyldioxirane (DMDO) with isobutane. The reaction involves hydrogen atom abstraction in the transition state, and trajectories branch to the oxygen rebound pathway, which gives tert-butanol and acetone, or a separated radical pair. In the gas phase, only 10% of the reactive trajectories undergo the oxygen rebound pathway, but this increases to 90% in simulations in an implicit acetone solvent (SMD) because the oxygen rebound becomes barrierless in solution. Short-lived diradical species were observed in the oxygen rebound trajectories. The time gap between C–H bond-breaking and C–O bond formation ranges from 30 to 150 fs, close to the
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chiral phosphoric acid catalyzed highly enantioselective desymmetrization of 2 substituted and 2 2 disubstituted 1 3 diols via oxidative cleavage of benzylidene acetals
ChemInform, 2015Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:This highly enantioselective reaction proceeds through formation of an “ortho ester” intermediate via oxidation of the 1,3-diol benzylidene acetal by Dimethyldioxirane and a subsequent proton transfer catalyzed by chiral phosphoric acids (CPA).
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chiral phosphoric acid catalyzed highly enantioselective desymmetrization of 2 substituted and 2 2 disubstituted 1 3 diols via oxidative cleavage of benzylidene acetals
Journal of the American Chemical Society, 2014Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:A highly enantioselective catalytic protocol for the desymmetrization of a wide variety of 2-substituted and 2,2-disubstituted 1,3-diols is reported. This reaction proceeds through the formation of an “ortho ester” intermediate via oxidation of 1,3-diol benzylidene acetal by Dimethyldioxirane (DMDO) and the subsequent proton transfer catalyzed by chiral phosphoric acid (CPA). The mechanism and origins of enantioselectivity of this reaction are identified using DFT calculations. The oxidation by DMDO is rate-determining, and the phosphoric acid significantly accelerates the proton transfer; the attractive interactions between the benzylidene part of the substrate and the 2,4,6-triisopropyl group of CPA are the key to high enantioselectivity.
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Chiral Phosphoric Acid Catalyzed Highly Enantioselective Desymmetrization of 2‑Substituted and 2,2-Disubstituted 1,3-Diols via Oxidative Cleavage of Benzylidene Acetals
2014Co-Authors: Shanshui Meng, Yong Liang, Kousen Cao, Lufeng Zou, Xingbang Lin, Hui Yang, K N Houk, Wenhua ZhengAbstract:A highly enantioselective catalytic protocol for the desymmetrization of a wide variety of 2-substituted and 2,2-disubstituted 1,3-diols is reported. This reaction proceeds through the formation of an “ortho ester” intermediate via oxidation of 1,3-diol benzylidene acetal by Dimethyldioxirane (DMDO) and the subsequent proton transfer catalyzed by chiral phosphoric acid (CPA). The mechanism and origins of enantioselectivity of this reaction are identified using DFT calculations. The oxidation by DMDO is rate-determining, and the phosphoric acid significantly accelerates the proton transfer; the attractive interactions between the benzylidene part of the substrate and the 2,4,6-triisopropyl group of CPA are the key to high enantioselectivity