The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Kendall N. Houk - One of the best experts on this subject based on the ideXlab platform.
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Cinchona urea catalyzed asymmetric sulfa michael reactions the bronsted acid hydrogen bonding model
Journal of the American Chemical Society, 2016Co-Authors: Matthew N Grayson, Kendall N. HoukAbstract:The Cinchona alkaloid-derived urea-catalyzed asymmetric conjugate addition of aromatic thiols to cycloalkenones was studied using density functional theory (DFT). Deprotonation of the thiol gives a protonated amine that activates the electrophile by Bronsted acid catalysis, while the urea group binds the nucleophilic thiolate by hydrogen bonding. These results demonstrate the generality of the Bronsted acid−hydrogen bonding transition state (TS) model for Cinchona alkaloid catalysis that we recently showed to be favored over Wynberg’s widely accepted ion pair−hydrogen bonding model and represent the first detailed mechanistic study of a Cinchona urea-catalyzed reaction. The conformation of the catalyst methoxy group has a strong effect on the TS, an effect overlooked in previous mechanistic studies of reactions catalyzed by Cinchona alkaloids.
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Cinchona alkaloid catalyzed asymmetric conjugate additions the bifunctional bronsted acid hydrogen bonding model
Journal of the American Chemical Society, 2016Co-Authors: Matthew N Grayson, Kendall N. HoukAbstract:Wynberg's report from 1977 that natural Cinchona alkaloids catalyze the asymmetric conjugate addition of aromatic thiols to cycloalkenones is a landmark discovery in hydrogen bonding organocatalysis. Wynberg proposed that this reaction proceeded via the formation of a thiolate-alkylammonium tight ion pair and activation of the enone electrophile by a hydrogen bond from the catalyst's hydroxyl group. This reaction model provided the mechanistic basis for understanding Wynberg's reaction and many other asymmetric transformations since. Our quantum mechanical calculations reveal a different model should be used to explain the results: the alkylammonium ion activates the enone by Bronsted acid catalysis, and the catalyst's hydroxyl group orients the thiolate nucleophile. The new model rationalizes the stereoselective outcome of Wynberg's reaction and provides a new, general model for asymmetric Cinchona organocatalysis.
Matthew N Grayson - One of the best experts on this subject based on the ideXlab platform.
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Cinchona urea catalyzed asymmetric sulfa michael reactions the bronsted acid hydrogen bonding model
Journal of the American Chemical Society, 2016Co-Authors: Matthew N Grayson, Kendall N. HoukAbstract:The Cinchona alkaloid-derived urea-catalyzed asymmetric conjugate addition of aromatic thiols to cycloalkenones was studied using density functional theory (DFT). Deprotonation of the thiol gives a protonated amine that activates the electrophile by Bronsted acid catalysis, while the urea group binds the nucleophilic thiolate by hydrogen bonding. These results demonstrate the generality of the Bronsted acid−hydrogen bonding transition state (TS) model for Cinchona alkaloid catalysis that we recently showed to be favored over Wynberg’s widely accepted ion pair−hydrogen bonding model and represent the first detailed mechanistic study of a Cinchona urea-catalyzed reaction. The conformation of the catalyst methoxy group has a strong effect on the TS, an effect overlooked in previous mechanistic studies of reactions catalyzed by Cinchona alkaloids.
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Cinchona alkaloid catalyzed asymmetric conjugate additions the bifunctional bronsted acid hydrogen bonding model
Journal of the American Chemical Society, 2016Co-Authors: Matthew N Grayson, Kendall N. HoukAbstract:Wynberg's report from 1977 that natural Cinchona alkaloids catalyze the asymmetric conjugate addition of aromatic thiols to cycloalkenones is a landmark discovery in hydrogen bonding organocatalysis. Wynberg proposed that this reaction proceeded via the formation of a thiolate-alkylammonium tight ion pair and activation of the enone electrophile by a hydrogen bond from the catalyst's hydroxyl group. This reaction model provided the mechanistic basis for understanding Wynberg's reaction and many other asymmetric transformations since. Our quantum mechanical calculations reveal a different model should be used to explain the results: the alkylammonium ion activates the enone by Bronsted acid catalysis, and the catalyst's hydroxyl group orients the thiolate nucleophile. The new model rationalizes the stereoselective outcome of Wynberg's reaction and provides a new, general model for asymmetric Cinchona organocatalysis.
Wei Wang - One of the best experts on this subject based on the ideXlab platform.
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highly enantioselective conjugate addition of nitroalkanes to enones catalyzed by Cinchona alkaloid derived primary amine
ChemInform, 2013Co-Authors: Wenjing Liu, Wenhu Duan, Wei Wang, Desheng MeiAbstract:Asymmetric Michael addition reaction of both acyclic and cyclic enones with nitroalkanes are catalyzed by a Cinchona alkaloid derivative to form adducts with up to 99% e.e.
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highly enantioselective conjugate addition of nitroalkanes to enones catalyzed by Cinchona alkaloid derived primary amine
Tetrahedron Letters, 2013Co-Authors: Wenjing Liu, Wenhu Duan, Wei Wang, Desheng MeiAbstract:Abstract A Cinchona alkaloid derived primary amine catalyzed conjugate addition of nitroalkanes to enones is described. The process affords the Michael adducts in good yield and with up to 99% ee for both acyclic and cyclic enones.
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Cinchona alkaloid based thiourea promoted enantioselective conjugate addition of n heterocycles to enones
Synthesis, 2007Co-Authors: Jian Wang, Hexin Xie, Wei WangAbstract:The first enantioselective conjugate addition reaction of 1 H-benzotriazole with a variety of enones has been developed. The process, catalyzed by a Cinchona alkaloid thiourea, affords Michael adducts in good yields and with moderate to good enantioselectivities.
Wenhu Duan - One of the best experts on this subject based on the ideXlab platform.
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highly enantioselective conjugate addition of nitroalkanes to enones catalyzed by Cinchona alkaloid derived primary amine
ChemInform, 2013Co-Authors: Wenjing Liu, Wenhu Duan, Wei Wang, Desheng MeiAbstract:Asymmetric Michael addition reaction of both acyclic and cyclic enones with nitroalkanes are catalyzed by a Cinchona alkaloid derivative to form adducts with up to 99% e.e.
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highly enantioselective conjugate addition of nitroalkanes to enones catalyzed by Cinchona alkaloid derived primary amine
Tetrahedron Letters, 2013Co-Authors: Wenjing Liu, Wenhu Duan, Wei Wang, Desheng MeiAbstract:Abstract A Cinchona alkaloid derived primary amine catalyzed conjugate addition of nitroalkanes to enones is described. The process affords the Michael adducts in good yield and with up to 99% ee for both acyclic and cyclic enones.
Yongjun Chen - One of the best experts on this subject based on the ideXlab platform.
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highly diastereo and enantioselective 3 2 annulation of isatin derived morita baylis hillman carbonates with trifluoropyruvate catalyzed by tertiary amines
Chemical Communications, 2013Co-Authors: Nengjun Zhong, Li Liu, Dong Wang, Feng Wei, Qingqing Xuan, Yongjun ChenAbstract:An enantioselective [3+2] annulation of Morita–Baylis–Hillman carbonates with trifluoropyruvate catalyzed by modified Cinchona alkaloids was developed in good to excellent yields with excellent diastereo- and enantioselectivities.
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highly enantioselective michael addition of 2 oxindoles to vinyl selenone in rtils catalyzed by a Cinchona alkaloid based thiourea
Chemical Communications, 2011Co-Authors: Tao Zhang, Liang Cheng, Shahid Hameed, Li Liu, Dong Wang, Yongjun ChenAbstract:A highly enantioselective Michael addition of 2-oxindoles (1) to vinyl selenone (2) in RTILs catalyzed by a Cinchona alkaloid-based thiourea has been developed in high yields (80–91%) with excellent enantioselectivities (up to 95% ee).