The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Kiyoshi Tomioka - One of the best experts on this subject based on the ideXlab platform.
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exploration of Dimethylzinc mediated radical reactions
ChemInform, 2015Co-Authors: Kenichi Yamada, Kiyoshi TomiokaAbstract:In this account, our studies on radical reactions that are promoted by Dimethylzinc and air are described. Advantages of this reagent and differences from conventional radical initiators, such as triethylborane, are discussed.
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stereoselective radical addition of an acetal to sterically tuned enantiomerically pure n sulfinyl imines
Chemical & Pharmaceutical Bulletin, 2010Co-Authors: Tito Akindele, Masaru Maekawa, Mayu Nakano, Yasutomo Yamamoto, Kenichi Yamada, Takumi Sejima, Kiyoshi TomiokaAbstract:Enantiomerically enriched sulfonamides were synthesized by the radical addition of an acetal to enantiomerically pure N-sulfinyl imines using Dimethylzinc-air and boron trifluoride diethyl etherate. Higher levels of stereocontrol were observed by using a mesitylenesulfinyl group. Furthermore, an amine and an amino alcohol with high enantiomeric purity were obtainable from the sulfonamide product.
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Dimethylzinc initiated radical reactions
ChemInform, 2009Co-Authors: Tito Akindele, Kenichi Yamada, Kiyoshi TomiokaAbstract:Developments in modern organic synthesis owe much to the field of radical chemistry. Mild reaction conditions, high selectivity, good functional group tolerance and high product yield are features that have made reactions involving radical species indispensable tools for synthetic chemists. In part, the discovery of new radical initiators has led to the efficiency that now characterizes most radical reactions. This Account describes our investigations of radical reactions initiated by Dimethylzinc. In 2001, we unexpectedly observed this reaction while investigating the amidophosphane-copper-catalyzed asymmetric addition of Dimethylzinc to N-sulfonyl imines with tetrahydrofuran (THF) as reaction solvent. However, instead of adding the desired methyl group to the N-sulfonyl imine, we produced the THF adduct in excellent yield. This result laid the foundation for our discovery of novel modes of reactivity. Further investigations of the unexpected addition reaction revealed that a trace amount of air was needed for reaction progress, indicating that radical intermediates were involved. Indeed, controlled injection of air into the reaction flask by a syringe pump through a sodium hydroxide tube afforded the products in good to excellent yield. In addition, the reaction proved to be chemoselective for a C=N bond over a C=O bond, as well as for 1,4-addition over 1,2-addition. We developed asymmetric variants of the radical addition reaction of ethers to imines using chiral N-sulfinyl imines to produce the adducts in reasonably high stereoselectivity (up to 11:1). A 93:7 diastereomeric ratio of the adduct was obtained when bis(8-phenylmenthyl) benzylidenemalonate was used in the radical addition of ethers to C=C bonds. Interestingly, in the presence of Dimethylzinc and air, arylamines, alkoxyamines, and dialkylhydrazines react with THF to give amino alcohols, oximes, and hydrazones, respectively, in moderate to high yields. We performed a tin-free intermolecular addition of functionalized primary alkyl groups, generated from their corresponding iodides, to N-sulfonyl imines using Dimethylzinc, air, boron trifluoride diethyl etherate, and a catalytic amount of copper(II) triflate. Direct C-H bond cleavage from cycloalkanes was also feasible in the presence of Dimethylzinc, air, and boron trifluoride diethyl etherate to give the corresponding cycloalkyl radicals, which were suitable nucleophiles for N-sulfonyl imines. In all of the above reactions, Dimethylzinc was a superior radical initiator than other conventional initiators such as dibenzoyl peroxide, diethylzinc, and triethylborane. We hope the coming decades will witness the report of other novel radical initiators that would complement the reactivity modes of existing ones.
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chemoselective conjugate addition of Dimethylzinc mediated ether and acetal radicals to alkylidenemalonates and asymmetric reactions
Journal of Organic Chemistry, 2008Co-Authors: Kenichi Yamada, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:Cyclic and acyclic ether or acetal radicals were generated directly from ethers or acetals by the action of Dimethylzinc-air, and their subsequent conjugate addition reaction with alkylidenemalonates afforded the corresponding conjugate adducts in reasonably high yields. The reaction with benzylidenemalonates bearing formyl and imino groups gave chemoselectively the conjugate addition products. The asymmetric reaction of bis(8-phenylmenthyl) benzylidenemalonate proceeded diastereoselectively to provide the adduct with 93:7 dr.
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conjugate addition reaction of thf 2 yl radical with α β unsaturated n tosyl imines using a Dimethylzinc air initiator
Tetrahedron, 2008Co-Authors: Kenichi Yamada, Hiroyuki Umeki, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:The reaction of tetrahydrofuran-2-yl radical, generated directly from THF by the action of Dimethylzinc–air, with α,β-unsaturated N-tosyl aldimines was demonstrated to proceed preferentially in a conjugate addition manner to give 2-(3-hydroxyalkyl)- or 2-(3-aminoalkyl)tetrahydrofurans in good yield. The slow addition of the enimines and the use of Dimethylzinc, rather than diethylzinc or triethylborane, were found to be the keys for the efficiency of the THF conjugate addition. The observed chemoselectivity could be rationalized by the larger coefficient of LUMO at the corresponding reaction site of the enimine.
Kenichi Yamada - One of the best experts on this subject based on the ideXlab platform.
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striking difference between succinimidomethyl and phthalimidomethyl radicals in conjugate addition to alkylidenemalonate initiated by Dimethylzinc
ChemInform, 2016Co-Authors: Kenichi Yamada, Yusuke Matsumoto, Shintaro Fujii, Takehito Konishi, Yousuke Yamaoka, Kiyosei TakasuAbstract:We used Dimethylzinc to develop a conjugate addition reaction of imidomethyl radicals to alkylidenemalonates, in which we observed a significant difference between succinimidomethyl and phthalimidomethyl radicals. This reaction provides new access to γ-aminobutyric acid derivatives, which often function as neurotransmitters.
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exploration of Dimethylzinc mediated radical reactions
ChemInform, 2015Co-Authors: Kenichi Yamada, Kiyoshi TomiokaAbstract:In this account, our studies on radical reactions that are promoted by Dimethylzinc and air are described. Advantages of this reagent and differences from conventional radical initiators, such as triethylborane, are discussed.
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stereoselective radical addition of an acetal to sterically tuned enantiomerically pure n sulfinyl imines
Chemical & Pharmaceutical Bulletin, 2010Co-Authors: Tito Akindele, Masaru Maekawa, Mayu Nakano, Yasutomo Yamamoto, Kenichi Yamada, Takumi Sejima, Kiyoshi TomiokaAbstract:Enantiomerically enriched sulfonamides were synthesized by the radical addition of an acetal to enantiomerically pure N-sulfinyl imines using Dimethylzinc-air and boron trifluoride diethyl etherate. Higher levels of stereocontrol were observed by using a mesitylenesulfinyl group. Furthermore, an amine and an amino alcohol with high enantiomeric purity were obtainable from the sulfonamide product.
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Dimethylzinc initiated radical reactions
ChemInform, 2009Co-Authors: Tito Akindele, Kenichi Yamada, Kiyoshi TomiokaAbstract:Developments in modern organic synthesis owe much to the field of radical chemistry. Mild reaction conditions, high selectivity, good functional group tolerance and high product yield are features that have made reactions involving radical species indispensable tools for synthetic chemists. In part, the discovery of new radical initiators has led to the efficiency that now characterizes most radical reactions. This Account describes our investigations of radical reactions initiated by Dimethylzinc. In 2001, we unexpectedly observed this reaction while investigating the amidophosphane-copper-catalyzed asymmetric addition of Dimethylzinc to N-sulfonyl imines with tetrahydrofuran (THF) as reaction solvent. However, instead of adding the desired methyl group to the N-sulfonyl imine, we produced the THF adduct in excellent yield. This result laid the foundation for our discovery of novel modes of reactivity. Further investigations of the unexpected addition reaction revealed that a trace amount of air was needed for reaction progress, indicating that radical intermediates were involved. Indeed, controlled injection of air into the reaction flask by a syringe pump through a sodium hydroxide tube afforded the products in good to excellent yield. In addition, the reaction proved to be chemoselective for a C=N bond over a C=O bond, as well as for 1,4-addition over 1,2-addition. We developed asymmetric variants of the radical addition reaction of ethers to imines using chiral N-sulfinyl imines to produce the adducts in reasonably high stereoselectivity (up to 11:1). A 93:7 diastereomeric ratio of the adduct was obtained when bis(8-phenylmenthyl) benzylidenemalonate was used in the radical addition of ethers to C=C bonds. Interestingly, in the presence of Dimethylzinc and air, arylamines, alkoxyamines, and dialkylhydrazines react with THF to give amino alcohols, oximes, and hydrazones, respectively, in moderate to high yields. We performed a tin-free intermolecular addition of functionalized primary alkyl groups, generated from their corresponding iodides, to N-sulfonyl imines using Dimethylzinc, air, boron trifluoride diethyl etherate, and a catalytic amount of copper(II) triflate. Direct C-H bond cleavage from cycloalkanes was also feasible in the presence of Dimethylzinc, air, and boron trifluoride diethyl etherate to give the corresponding cycloalkyl radicals, which were suitable nucleophiles for N-sulfonyl imines. In all of the above reactions, Dimethylzinc was a superior radical initiator than other conventional initiators such as dibenzoyl peroxide, diethylzinc, and triethylborane. We hope the coming decades will witness the report of other novel radical initiators that would complement the reactivity modes of existing ones.
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chemoselective conjugate addition of Dimethylzinc mediated ether and acetal radicals to alkylidenemalonates and asymmetric reactions
Journal of Organic Chemistry, 2008Co-Authors: Kenichi Yamada, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:Cyclic and acyclic ether or acetal radicals were generated directly from ethers or acetals by the action of Dimethylzinc-air, and their subsequent conjugate addition reaction with alkylidenemalonates afforded the corresponding conjugate adducts in reasonably high yields. The reaction with benzylidenemalonates bearing formyl and imino groups gave chemoselectively the conjugate addition products. The asymmetric reaction of bis(8-phenylmenthyl) benzylidenemalonate proceeded diastereoselectively to provide the adduct with 93:7 dr.
Yasutomo Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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stereoselective radical addition of an acetal to sterically tuned enantiomerically pure n sulfinyl imines
Chemical & Pharmaceutical Bulletin, 2010Co-Authors: Tito Akindele, Masaru Maekawa, Mayu Nakano, Yasutomo Yamamoto, Kenichi Yamada, Takumi Sejima, Kiyoshi TomiokaAbstract:Enantiomerically enriched sulfonamides were synthesized by the radical addition of an acetal to enantiomerically pure N-sulfinyl imines using Dimethylzinc-air and boron trifluoride diethyl etherate. Higher levels of stereocontrol were observed by using a mesitylenesulfinyl group. Furthermore, an amine and an amino alcohol with high enantiomeric purity were obtainable from the sulfonamide product.
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chemoselective conjugate addition of Dimethylzinc mediated ether and acetal radicals to alkylidenemalonates and asymmetric reactions
Journal of Organic Chemistry, 2008Co-Authors: Kenichi Yamada, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:Cyclic and acyclic ether or acetal radicals were generated directly from ethers or acetals by the action of Dimethylzinc-air, and their subsequent conjugate addition reaction with alkylidenemalonates afforded the corresponding conjugate adducts in reasonably high yields. The reaction with benzylidenemalonates bearing formyl and imino groups gave chemoselectively the conjugate addition products. The asymmetric reaction of bis(8-phenylmenthyl) benzylidenemalonate proceeded diastereoselectively to provide the adduct with 93:7 dr.
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conjugate addition reaction of thf 2 yl radical with α β unsaturated n tosyl imines using a Dimethylzinc air initiator
Tetrahedron, 2008Co-Authors: Kenichi Yamada, Hiroyuki Umeki, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:The reaction of tetrahydrofuran-2-yl radical, generated directly from THF by the action of Dimethylzinc–air, with α,β-unsaturated N-tosyl aldimines was demonstrated to proceed preferentially in a conjugate addition manner to give 2-(3-hydroxyalkyl)- or 2-(3-aminoalkyl)tetrahydrofurans in good yield. The slow addition of the enimines and the use of Dimethylzinc, rather than diethylzinc or triethylborane, were found to be the keys for the efficiency of the THF conjugate addition. The observed chemoselectivity could be rationalized by the larger coefficient of LUMO at the corresponding reaction site of the enimine.
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asymmetric radical addition of ethers to enantiopure n p toluenesulfinyl aldimines mediated by Dimethylzinc air
ChemInform, 2007Co-Authors: Tito Akindele, Hiroyuki Umeki, Masaru Maekawa, Yasutomo Yamamoto, Kenichi Yamada, Kiyoshi TomiokaAbstract:Asymmetric radical addition of ethers to enantiopure aromatic N-p-toluenesulfinyl aldimines has been achieved. The requisite radicals were generated by Dimethylzinc−air. Lewis acid activation of the N-p-toluenesulfinyl aldimines followed by radical addition gives a mixture of sulfinamide and sulfonamide products. Subsequent treatment of the mixture with dry m-CPBA affords the sulfonamide product in enantiomerically enriched form.
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tin free intermolecular addition of primary alkyls to imines via the Dimethylzinc air radical process
Organic Letters, 2006Co-Authors: Kenichi Yamada, Hiroyuki Umeki, Masaru Maekawa, Tito Akindele, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:[reaction: see text] A Dimethylzinc-air initiator was applied to the generation of primary alkyl radicals from alkyl iodides. The addition of the generated primary alkyl radicals to N-tosylimines was accelerated by the action of boron trifluoride-diethyl etherate and copper(II) triflate to give the corresponding adducts in good yields after 2-3 h. Air oxygen was essential for the reaction to proceed, showing involvement of a radical process in the reaction.
Masaru Maekawa - One of the best experts on this subject based on the ideXlab platform.
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stereoselective radical addition of an acetal to sterically tuned enantiomerically pure n sulfinyl imines
Chemical & Pharmaceutical Bulletin, 2010Co-Authors: Tito Akindele, Masaru Maekawa, Mayu Nakano, Yasutomo Yamamoto, Kenichi Yamada, Takumi Sejima, Kiyoshi TomiokaAbstract:Enantiomerically enriched sulfonamides were synthesized by the radical addition of an acetal to enantiomerically pure N-sulfinyl imines using Dimethylzinc-air and boron trifluoride diethyl etherate. Higher levels of stereocontrol were observed by using a mesitylenesulfinyl group. Furthermore, an amine and an amino alcohol with high enantiomeric purity were obtainable from the sulfonamide product.
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chemoselective conjugate addition of Dimethylzinc mediated ether and acetal radicals to alkylidenemalonates and asymmetric reactions
Journal of Organic Chemistry, 2008Co-Authors: Kenichi Yamada, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:Cyclic and acyclic ether or acetal radicals were generated directly from ethers or acetals by the action of Dimethylzinc-air, and their subsequent conjugate addition reaction with alkylidenemalonates afforded the corresponding conjugate adducts in reasonably high yields. The reaction with benzylidenemalonates bearing formyl and imino groups gave chemoselectively the conjugate addition products. The asymmetric reaction of bis(8-phenylmenthyl) benzylidenemalonate proceeded diastereoselectively to provide the adduct with 93:7 dr.
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conjugate addition reaction of thf 2 yl radical with α β unsaturated n tosyl imines using a Dimethylzinc air initiator
Tetrahedron, 2008Co-Authors: Kenichi Yamada, Hiroyuki Umeki, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:The reaction of tetrahydrofuran-2-yl radical, generated directly from THF by the action of Dimethylzinc–air, with α,β-unsaturated N-tosyl aldimines was demonstrated to proceed preferentially in a conjugate addition manner to give 2-(3-hydroxyalkyl)- or 2-(3-aminoalkyl)tetrahydrofurans in good yield. The slow addition of the enimines and the use of Dimethylzinc, rather than diethylzinc or triethylborane, were found to be the keys for the efficiency of the THF conjugate addition. The observed chemoselectivity could be rationalized by the larger coefficient of LUMO at the corresponding reaction site of the enimine.
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asymmetric radical addition of ethers to enantiopure n p toluenesulfinyl aldimines mediated by Dimethylzinc air
ChemInform, 2007Co-Authors: Tito Akindele, Hiroyuki Umeki, Masaru Maekawa, Yasutomo Yamamoto, Kenichi Yamada, Kiyoshi TomiokaAbstract:Asymmetric radical addition of ethers to enantiopure aromatic N-p-toluenesulfinyl aldimines has been achieved. The requisite radicals were generated by Dimethylzinc−air. Lewis acid activation of the N-p-toluenesulfinyl aldimines followed by radical addition gives a mixture of sulfinamide and sulfonamide products. Subsequent treatment of the mixture with dry m-CPBA affords the sulfonamide product in enantiomerically enriched form.
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tin free intermolecular addition of primary alkyls to imines via the Dimethylzinc air radical process
Organic Letters, 2006Co-Authors: Kenichi Yamada, Hiroyuki Umeki, Masaru Maekawa, Tito Akindele, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:[reaction: see text] A Dimethylzinc-air initiator was applied to the generation of primary alkyl radicals from alkyl iodides. The addition of the generated primary alkyl radicals to N-tosylimines was accelerated by the action of boron trifluoride-diethyl etherate and copper(II) triflate to give the corresponding adducts in good yields after 2-3 h. Air oxygen was essential for the reaction to proceed, showing involvement of a radical process in the reaction.
Tito Akindele - One of the best experts on this subject based on the ideXlab platform.
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stereoselective radical addition of an acetal to sterically tuned enantiomerically pure n sulfinyl imines
Chemical & Pharmaceutical Bulletin, 2010Co-Authors: Tito Akindele, Masaru Maekawa, Mayu Nakano, Yasutomo Yamamoto, Kenichi Yamada, Takumi Sejima, Kiyoshi TomiokaAbstract:Enantiomerically enriched sulfonamides were synthesized by the radical addition of an acetal to enantiomerically pure N-sulfinyl imines using Dimethylzinc-air and boron trifluoride diethyl etherate. Higher levels of stereocontrol were observed by using a mesitylenesulfinyl group. Furthermore, an amine and an amino alcohol with high enantiomeric purity were obtainable from the sulfonamide product.
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Dimethylzinc initiated radical reactions
ChemInform, 2009Co-Authors: Tito Akindele, Kenichi Yamada, Kiyoshi TomiokaAbstract:Developments in modern organic synthesis owe much to the field of radical chemistry. Mild reaction conditions, high selectivity, good functional group tolerance and high product yield are features that have made reactions involving radical species indispensable tools for synthetic chemists. In part, the discovery of new radical initiators has led to the efficiency that now characterizes most radical reactions. This Account describes our investigations of radical reactions initiated by Dimethylzinc. In 2001, we unexpectedly observed this reaction while investigating the amidophosphane-copper-catalyzed asymmetric addition of Dimethylzinc to N-sulfonyl imines with tetrahydrofuran (THF) as reaction solvent. However, instead of adding the desired methyl group to the N-sulfonyl imine, we produced the THF adduct in excellent yield. This result laid the foundation for our discovery of novel modes of reactivity. Further investigations of the unexpected addition reaction revealed that a trace amount of air was needed for reaction progress, indicating that radical intermediates were involved. Indeed, controlled injection of air into the reaction flask by a syringe pump through a sodium hydroxide tube afforded the products in good to excellent yield. In addition, the reaction proved to be chemoselective for a C=N bond over a C=O bond, as well as for 1,4-addition over 1,2-addition. We developed asymmetric variants of the radical addition reaction of ethers to imines using chiral N-sulfinyl imines to produce the adducts in reasonably high stereoselectivity (up to 11:1). A 93:7 diastereomeric ratio of the adduct was obtained when bis(8-phenylmenthyl) benzylidenemalonate was used in the radical addition of ethers to C=C bonds. Interestingly, in the presence of Dimethylzinc and air, arylamines, alkoxyamines, and dialkylhydrazines react with THF to give amino alcohols, oximes, and hydrazones, respectively, in moderate to high yields. We performed a tin-free intermolecular addition of functionalized primary alkyl groups, generated from their corresponding iodides, to N-sulfonyl imines using Dimethylzinc, air, boron trifluoride diethyl etherate, and a catalytic amount of copper(II) triflate. Direct C-H bond cleavage from cycloalkanes was also feasible in the presence of Dimethylzinc, air, and boron trifluoride diethyl etherate to give the corresponding cycloalkyl radicals, which were suitable nucleophiles for N-sulfonyl imines. In all of the above reactions, Dimethylzinc was a superior radical initiator than other conventional initiators such as dibenzoyl peroxide, diethylzinc, and triethylborane. We hope the coming decades will witness the report of other novel radical initiators that would complement the reactivity modes of existing ones.
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chemoselective conjugate addition of Dimethylzinc mediated ether and acetal radicals to alkylidenemalonates and asymmetric reactions
Journal of Organic Chemistry, 2008Co-Authors: Kenichi Yamada, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:Cyclic and acyclic ether or acetal radicals were generated directly from ethers or acetals by the action of Dimethylzinc-air, and their subsequent conjugate addition reaction with alkylidenemalonates afforded the corresponding conjugate adducts in reasonably high yields. The reaction with benzylidenemalonates bearing formyl and imino groups gave chemoselectively the conjugate addition products. The asymmetric reaction of bis(8-phenylmenthyl) benzylidenemalonate proceeded diastereoselectively to provide the adduct with 93:7 dr.
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conjugate addition reaction of thf 2 yl radical with α β unsaturated n tosyl imines using a Dimethylzinc air initiator
Tetrahedron, 2008Co-Authors: Kenichi Yamada, Hiroyuki Umeki, Masaru Maekawa, Tito Akindele, Mayu Nakano, Yasutomo Yamamoto, Kiyoshi TomiokaAbstract:The reaction of tetrahydrofuran-2-yl radical, generated directly from THF by the action of Dimethylzinc–air, with α,β-unsaturated N-tosyl aldimines was demonstrated to proceed preferentially in a conjugate addition manner to give 2-(3-hydroxyalkyl)- or 2-(3-aminoalkyl)tetrahydrofurans in good yield. The slow addition of the enimines and the use of Dimethylzinc, rather than diethylzinc or triethylborane, were found to be the keys for the efficiency of the THF conjugate addition. The observed chemoselectivity could be rationalized by the larger coefficient of LUMO at the corresponding reaction site of the enimine.
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asymmetric radical addition of ethers to enantiopure n p toluenesulfinyl aldimines mediated by Dimethylzinc air
ChemInform, 2007Co-Authors: Tito Akindele, Hiroyuki Umeki, Masaru Maekawa, Yasutomo Yamamoto, Kenichi Yamada, Kiyoshi TomiokaAbstract:Asymmetric radical addition of ethers to enantiopure aromatic N-p-toluenesulfinyl aldimines has been achieved. The requisite radicals were generated by Dimethylzinc−air. Lewis acid activation of the N-p-toluenesulfinyl aldimines followed by radical addition gives a mixture of sulfinamide and sulfonamide products. Subsequent treatment of the mixture with dry m-CPBA affords the sulfonamide product in enantiomerically enriched form.