The Experts below are selected from a list of 17403 Experts worldwide ranked by ideXlab platform
Masakatsu Shibasaki - One of the best experts on this subject based on the ideXlab platform.
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direct catalytic asymmetric addition of allyl cyanide to ketones via soft Lewis acid hard bronsted Base hard Lewis Base catalysis
Journal of the American Chemical Society, 2010Co-Authors: Ryo Yazaki, Naoya Kumagai, Masakatsu ShibasakiAbstract:We report that a hard Lewis Base substantially affects the reaction efficiency of direct catalytic asymmetric gamma-addition of allyl cyanide (1a) to ketones promoted by a soft Lewis acid/hard Bronsted Base catalyst. Mechanistic studies have revealed that Cu/(R,R)-Ph-BPE and Li(OC(6)H(4)-p-OMe) serve as a soft Lewis acid and a hard Bronsted Base, respectively, allowing for deprotonative activation of 1a as the rate-determining step. A ternary catalytic system comprising a soft Lewis acid/hard Bronsted Base and an additional hard Lewis Base, in which the basicity of the hard Bronsted Base Li(OC(6)H(4)-p-OMe) was enhanced by phosphine oxide (the hard Lewis Base) through a hard-hard interaction, outperformed the previously developed binary soft Lewis acid/hard Bronsted Base catalytic system, leading to higher yields and enantioselectivities while using one-tenth the catalyst loading and one-fifth the amount of 1a. This second-generation catalyst allows efficient access to highly enantioenriched tertiary alcohols under nearly ideal atom-economical conditions (0.5-1 mol % catalyst loading and a substrate molar ratio of 1:2).
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direct catalytic asymmetric addition of allyl cyanide to ketones via soft Lewis acid hard bronsted Base hard Lewis Base catalysis
Journal of the American Chemical Society, 2010Co-Authors: Ryo Yazaki, Naoya Kumagai, Masakatsu ShibasakiAbstract:We report that a hard Lewis Base substantially affects the reaction efficiency of direct catalytic asymmetric γ-addition of allyl cyanide (1a) to ketones promoted by a soft Lewis acid/hard Bronsted Base catalyst. Mechanistic studies have revealed that Cu/(R,R)-Ph-BPE and Li(OC6H4-p-OMe) serve as a soft Lewis acid and a hard Bronsted Base, respectively, allowing for deprotonative activation of 1a as the rate-determining step. A ternary catalytic system comprising a soft Lewis acid/hard Bronsted Base and an additional hard Lewis Base, in which the basicity of the hard Bronsted Base Li(OC6H4-p-OMe) was enhanced by phosphine oxide (the hard Lewis Base) through a hard−hard interaction, outperformed the previously developed binary soft Lewis acid/hard Bronsted Base catalytic system, leading to higher yields and enantioselectivities while using one-tenth the catalyst loading and one-fifth the amount of 1a. This second-generation catalyst allows efficient access to highly enantioenriched tertiary alcohols under n...
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power of cooperativity Lewis acid Lewis Base bifunctional asymmetric catalysis
Synlett, 2005Co-Authors: Motomu Kanai, Nobuki Kato, Eiko Ichikawa, Masakatsu ShibasakiAbstract:The concept of bifunctional asymmetric catalysis is very powerful for designing new enantioselective catalysts. We describe our investigation starting with the development of a BINOL-derived Lewis acid-Lewis Base bifunctional asymmetric catalyst for cyanosilylation of aldehydes. The initial establishment of the concept was followed by the development of new sugar-derived catalysts that promote general catalytic enantioselective cyanosilylation of ketones. We also describe the catalytic enantioselective Reissert reaction of pyridine derivatives and Strecker reaction of ketoimines as recent advances in this field.
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new entries in Lewis acid Lewis Base bifunctional asymmetric catalyst catalytic enantioselective reissert reaction of pyridine derivatives
Journal of the American Chemical Society, 2004Co-Authors: Eiko Ichikawa, Motomu Kanai, Masato Suzuki, Kazuo Yabu, Matthias Albert, Masakatsu ShibasakiAbstract:The first catalytic enantioselective Reissert reaction of pyridine derivatives that affords products with excellent regio- and enantioselectivity is described. The key for success is the development of new Lewis acid−Lewis Base bifunctional asymmetric catalysts containing an aluminum as a Lewis acid and sulfoxides or phosphine sulfides as a Lewis Base. These reactions are useful for the synthesis of a variety of chiral piperidine subunits, and catalytic enantioselective formal synthesis of CP-293,019, a selective D4 receptor antagonist, was achieved. Preliminary mechanistic studies indicated that both sulfoxides and phosphine sulfides can activate TMSCN as a Lewis Base. In addition, the sulfoxides with appropriate stereochemistry might stabilize a highly enantioselective bimetallic complex (a presumed active catalyst) through internal coordination to aluminum.
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highly enantioselective cyanosilylation of aldehydes catalyzed by a Lewis acid Lewis Base bifunctional catalyst
Tetrahedron, 2001Co-Authors: Yoshitaka Hamashima, Daisuke Sawada, Motomu Kanai, Hiroyuki Nogami, Masakatsu ShibasakiAbstract:Abstract A new bifunctional asymmetric catalyst containing a Lewis acid and a Lewis Base ( 1 ) was developed and applied to the catalytic asymmetric cyanosilylation of aldehydes. The products were obtained generally with excellent enantiomeric excess. The experiments using the control catalyst ( 5 ) and the catalyst containing more electron-rich phosphine oxide ( 6 ) suggest that the catalyst 1 should promote the reaction via a dual activation of the aldehyde by the aluminum and TMSCN by the phosphine oxide. This reaction is practical and was applied to the catalytic asymmetric total synthesis of epothilone A.
Scott E. Denmark - One of the best experts on this subject based on the ideXlab platform.
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Lewis Base Catalyzed, Enantioselective, Intramolecular Sulfenoamination of Olefins
2015Co-Authors: Scott E. Denmark, Hyung Min ChiAbstract:A method for the enantioselective, intramolecular sulfenoamination of various olefins has been developed using a chiral BINAM-Based selenophosphoramide, Lewis Base catalyst. Terminal and trans disubstituted alkenes afforded pyrrolidines, piperidines, and azepanes in high yields and high enantiomeric ratios via enantioselective formation and subsequent stereospecific capture of the thiiranium intermediate with the pendant tosyl-protected amine
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development and mechanism of an enantioselective bromocycloetherification reaction via Lewis Base chiral bronsted acid cooperative catalysis
Chirality, 2014Co-Authors: Scott E. Denmark, Matthew T BurkAbstract:The development of a binary catalyst system for bromocycloetherification, consisting of an achiral Lewis Base and a chiral Bronsted acid, is described in detail. The results of preliminary kinetic studies are also presented.
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Lewis Base catalyzed enantioselective intramolecular sulfenoamination of olefins
Journal of the American Chemical Society, 2014Co-Authors: Scott E. Denmark, Hyung Min ChiAbstract:A method for the enantioselective, intramolecular sulfenoamination of various olefins has been developed using a chiral BINAM-Based selenophosphoramide, Lewis Base catalyst. Terminal and trans disubstituted alkenes afforded pyrrolidines, piperidines, and azepanes in high yields and high enantiomeric ratios via enantioselective formation and subsequent stereospecific capture of the thiiranium intermediate with the pendant tosyl-protected amine.
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Lewis Base catalysis of the mukaiyama directed aldol reaction 40 years of inspiration and advances
Angewandte Chemie, 2013Co-Authors: Gregory L Beutner, Scott E. DenmarkAbstract:: Since the landmark publications of the first directed aldol addition reaction in 1973, the site, diastereo-, and enantioselective aldol reaction has been elevated to the rarefied status of being both a named and a strategy-level reaction (the Mukaiyama directed aldol reaction). The importance of this reaction in the stereoselective synthesis of untold numbers of organic compounds, both natural and unnatural, cannot be overstated. However, its impact on the field extends beyond the impressive applications in synthesis. The directed aldol reaction has served as a fertile proving ground for new concepts and new methods for stereocontrol and catalysis. This Minireview provides a case history of how the challenges of merging site selectivity, diastereoselectivity, enantioselectivity, and catalysis into a unified reaction manifold stimulated the development of Lewis Base catalyzed aldol addition reactions. The evolution of this process is chronicled from the authors' laboratories as well as in those of Professor Teruaki Mukaiyama.
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enantioselective bromocycloetherification by Lewis Base chiral bronsted acid cooperative catalysis
Organic Letters, 2012Co-Authors: Scott E. Denmark, Matthew T BurkAbstract:A binary catalyst system for the enantioselective bromocycloetherification of 5-arylpentenols is described. The combination of an achiral Lewis Base and a chiral Bronsted acid affords good enantioselectivities for the cyclization of Z configured 5-arylpentenols to form bromomethyltetrahydrofurans. The constitutional site selectivity is highly dependent upon the aromatic substituent and the configuration of the double bond.
Matthew T Burk - One of the best experts on this subject based on the ideXlab platform.
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development and mechanism of an enantioselective bromocycloetherification reaction via Lewis Base chiral bronsted acid cooperative catalysis
Chirality, 2014Co-Authors: Scott E. Denmark, Matthew T BurkAbstract:The development of a binary catalyst system for bromocycloetherification, consisting of an achiral Lewis Base and a chiral Bronsted acid, is described in detail. The results of preliminary kinetic studies are also presented.
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enantioselective bromocycloetherification by Lewis Base chiral bronsted acid cooperative catalysis
Organic Letters, 2012Co-Authors: Scott E. Denmark, Matthew T BurkAbstract:A binary catalyst system for the enantioselective bromocycloetherification of 5-arylpentenols is described. The combination of an achiral Lewis Base and a chiral Bronsted acid affords good enantioselectivities for the cyclization of Z configured 5-arylpentenols to form bromomethyltetrahydrofurans. The constitutional site selectivity is highly dependent upon the aromatic substituent and the configuration of the double bond.
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Lewis Base catalysis of bromo and iodolactonization and cycloetherification
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Scott E. Denmark, Matthew T BurkAbstract:Lewis Base catalyzed bromo- and iodolactonization reactions have been developed and the effects of catalyst structure on rate and cyclization selectivity have been systematically explored. The effects of substrate structure on halolactonization reactions and the interaction of those effects with the effects of catalyst structure have been investigated, leading to synthetically useful improvements in cyclization selectivity. The knowledge acquired was applied to the development of Lewis Base catalyzed bromo- and iodocycloetherification reactions. The ability of some of the surveyed catalysts to influence the cyclization selectivity of halolactonization reactions demonstrates their presence in the transition structure of the product-determining cyclization step. This observation implies that chiral derivatives of these catalysts have the potential to provide enantioenriched products regardless of the rates or mechanisms of halonium ion racemization.
Kazuaki Ishihara - One of the best experts on this subject based on the ideXlab platform.
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halogen bonding interaction between i2 and n iodosuccinimide in Lewis Base catalyzed iodolactonization
Organic Letters, 2020Co-Authors: Takahiro Horibe, Yasutaka Tsuji, Kazuaki IshiharaAbstract:The halogen-bonding interaction between I2 and N-iodosuccinimide (NIS) stabilized by a Lewis Base (LB) has been explored. 1H NMR, nuclear Overhauser effect (NOE), and diffusion-ordered NMR spectros...
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Thiourea–I2 as Lewis Base–Lewis Acid Cooperative Catalysts for Iodochlorination of Alkene with In Situ-Generated I–Cl
2018Co-Authors: Takahiro Horibe, Yasutaka Tsuji, Kazuaki IshiharaAbstract:Thiourea–I2 as Lewis Base–Lewis acid cooperative catalysts are developed for the iodochlorination of alkenes with in situ-generated iodine monochloride (I–Cl). The Lewis Base–Lewis acid cooperative system is sufficient to generate I–Cl from I2 with a chlorinating reagent at low temperature. Based on the solid-state structure of the active species, thiourea–I2 cooperatively captures I–Cl. By taking advantage of I–Cl generation and the control of I–Cl at low temperature, the thiourea–I2 cooperative system suppresses side reactions that arise from highly reactive free I–Cl
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enantioselective cyano alkoxycarbonylation of α oxoesters promoted by bronsted acid Lewis Base cooperative catalysts
Organic Letters, 2015Co-Authors: Kazuaki Ishihara, Yoshihiro OguraAbstract:The highly enantioselective cyano-alkoxycarbonylation of α-oxoesters with alkyl cyanoformates is promoted by a new chiral Bronsted acid–Lewis Base cooperative organocatalyst. The present catalysis can be performed at room temperature under nitrogen or air.
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chiral Lewis Base assisted bronsted acid lbba catalyzed enantioselective cyclization of 2 geranylphenols
Organic Letters, 2011Co-Authors: Akira Sakakura, Masayuki Sakuma, Kazuaki IshiharaAbstract:Chiral Lewis Base-assisted Bronsted acids (Chiral LBBAs) have been designed as new organocatalysts for biomimetic enantioselective cyclization. A salt of a chiral phosphonous acid diester with FSO3H catalyzes the enantioselective cyclization of 2-geranylphenols to give the desired trans-fused cyclized products with high diastereo- and enantioselectivities (up to 98:2 dr and 93% ee).
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sodium phenoxide phosphine oxides as extremely active Lewis Base catalysts for the mukaiyama aldol reaction with ketones
ChemInform, 2008Co-Authors: Manabu Hatano, Eri Takagi, Kazuaki IshiharaAbstract:A highly efficient Mukaiyama aldol reaction between ketones and trimethylsilyl enolates catalyzed by sodium phenoxide-phosphine oxides as simple homogeneous Lewis Base catalysts (0.5-10 mol %) was developed, which minimized competing retro-aldol reaction. For a variety of aromatic ketones and aldimines, aldol and Mannich-type products with an alpha-quaternary carbon center were obtained in good to excellent yields. Up to 100 mmol scale of benzophenone and trimethylsilyl enolate with 0.5 mol % of catalyst was established in 97% yield (34.8 g).
Ryo Yazaki - One of the best experts on this subject based on the ideXlab platform.
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direct catalytic asymmetric addition of allyl cyanide to ketones via soft Lewis acid hard bronsted Base hard Lewis Base catalysis
Journal of the American Chemical Society, 2010Co-Authors: Ryo Yazaki, Naoya Kumagai, Masakatsu ShibasakiAbstract:We report that a hard Lewis Base substantially affects the reaction efficiency of direct catalytic asymmetric γ-addition of allyl cyanide (1a) to ketones promoted by a soft Lewis acid/hard Bronsted Base catalyst. Mechanistic studies have revealed that Cu/(R,R)-Ph-BPE and Li(OC6H4-p-OMe) serve as a soft Lewis acid and a hard Bronsted Base, respectively, allowing for deprotonative activation of 1a as the rate-determining step. A ternary catalytic system comprising a soft Lewis acid/hard Bronsted Base and an additional hard Lewis Base, in which the basicity of the hard Bronsted Base Li(OC6H4-p-OMe) was enhanced by phosphine oxide (the hard Lewis Base) through a hard−hard interaction, outperformed the previously developed binary soft Lewis acid/hard Bronsted Base catalytic system, leading to higher yields and enantioselectivities while using one-tenth the catalyst loading and one-fifth the amount of 1a. This second-generation catalyst allows efficient access to highly enantioenriched tertiary alcohols under n...
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direct catalytic asymmetric addition of allyl cyanide to ketones via soft Lewis acid hard bronsted Base hard Lewis Base catalysis
Journal of the American Chemical Society, 2010Co-Authors: Ryo Yazaki, Naoya Kumagai, Masakatsu ShibasakiAbstract:We report that a hard Lewis Base substantially affects the reaction efficiency of direct catalytic asymmetric gamma-addition of allyl cyanide (1a) to ketones promoted by a soft Lewis acid/hard Bronsted Base catalyst. Mechanistic studies have revealed that Cu/(R,R)-Ph-BPE and Li(OC(6)H(4)-p-OMe) serve as a soft Lewis acid and a hard Bronsted Base, respectively, allowing for deprotonative activation of 1a as the rate-determining step. A ternary catalytic system comprising a soft Lewis acid/hard Bronsted Base and an additional hard Lewis Base, in which the basicity of the hard Bronsted Base Li(OC(6)H(4)-p-OMe) was enhanced by phosphine oxide (the hard Lewis Base) through a hard-hard interaction, outperformed the previously developed binary soft Lewis acid/hard Bronsted Base catalytic system, leading to higher yields and enantioselectivities while using one-tenth the catalyst loading and one-fifth the amount of 1a. This second-generation catalyst allows efficient access to highly enantioenriched tertiary alcohols under nearly ideal atom-economical conditions (0.5-1 mol % catalyst loading and a substrate molar ratio of 1:2).
