The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Víctor S. Martín - One of the best experts on this subject based on the ideXlab platform.
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[1,3]‐Transfer of Chirality during the Nicholas Reaction in γ‐Benzyloxy Propargylic Alcohols
Chemistry (Weinheim an der Bergstrasse Germany), 2006Co-Authors: David Díaz Díaz, Miguel A. Ramirez, Víctor S. MartínAbstract:A highly regio- and stereoselective intramolecular [1,5]-hydrogen-transfer process is described. Treatment of gamma-benzyl-protected Co2(CO)6-alpha,gamma-acetylenic diols with BF3 x OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether Group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the Benzyloxy Group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair-like transition state substantiated by a theoretical study is also included.
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Asymmetric synthesis of the (2S,4S,6S)-2,4,6-trimethylnonyl subunit of siphonarienes
Israel Journal of Chemistry, 2001Co-Authors: David Díaz Díaz, Fernando R. Pinacho Crisóstomo, Víctor S. MartínAbstract:The paper describes an asymmetric approach to the synthesis of the (2S,4S,6S)-2,4,6-trimethylnonyl segment of siphonarienes. The key step used is a newly developed methodology to obtain sec-dialkyl acetylenes based on theintramolecular hydride transfer from a secondary γ-Benzyloxy Group with well-defined absolute stereochemistry, ensured by a Sharpless asymmetric epoxidation reaction, to a cation generated by Lewis acid treatment of a tertiary Co 2 (CO) 6 -complexed propargylic alcohol.
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Enantioselective synthesis of alkyl-branched alkanes. Synthesis Of the stereoisomers of 7,11-dimethylheptadecane and 7-methylheptadecane, components of the pheromone of lambdina species
The Journal of organic chemistry, 2000Co-Authors: David Díaz Díaz, Víctor S. MartínAbstract:The stereoisomers of 7,11-dimethylheptadecane and 7-methylheptadecane have been synthesized. The key step used has been the intramolecular hydride transfer from a secondary gamma-Benzyloxy Group with defined absolute stereochemistry to a cation generated by Lewis acid treatment of the suitable tertiary Co(2)(CO)(6)-complexed propargylic alcohol. The application of this method provided stereochemically defined alpha-alkyl-gamma-hydroxy-acetylenes that after hydrogenation and further reductive elimination of the hydroxyl Group yielded sec-alkyl hydrocarbons.
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Enantiocontrolled synthesis of trialkyl-substituted stereogenic carbons. A general route to cis-3,5-dialkyl gamma-lactones
Organic letters, 2000Co-Authors: David Díaz Díaz, Víctor S. MartínAbstract:Lewis acid treatment of tertiary Co2(CO)6-propargylic alcohols having a stereochemically defined Benzyloxy Group at the γ-benzyl position yielded after cobalt demetalation sec-dialkyl bishomopropargylic alcohols in good yields. The reaction is highly stereoselective and predictable, providing pure stereoisomers. The use of benzyl-α,α‘-d2 ethers permitted the stereoselective d-labeling of methines and methylenes. Very simple chemical manipulations provided a general methodology to obtain the enantiomers of 3,5-dialkyl-γ-lactones.
Kiyoshi Arai - One of the best experts on this subject based on the ideXlab platform.
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Novel glycol benzyl ether herbicides: Herbicidal activity of 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran derivatives
Journal of Pesticide Science, 2006Co-Authors: Takeshi Kakimoto, Fumiaki Koizumi, Kangetsu Hirase, Kiyoshi AraiAbstract:The structure–activity relationship of novel glycol benzyl ether herbicides, 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyrans (TFBs), was elucidated. Herbicidal activity against Echinochloa crus-galli and rice injury varied with substituents of the Benzyloxy Group at C-3. When substituents other than the Benzyloxy Group, such as the cyclohexylmethyloxy Group or the benzoyloxy Group, were introduced, the herbicidal activity of TFBs was reduced. Introduction of an (S)-methyl Group at C-5 increased herbicidal activity but aggravated rice injury. When comparing the herbicidal activity of two stereoisomers, the 5-(S)-isomer showed stronger herbicidal activity than the 5-(R)-isomer. Even when the benzene ring of the fused ring system of TFB was replaced by thiophene or furan, high herbicidal activity was manifested. In particular, TFB partly replaced by thiophene showed the highest herbicidal activity among all compounds examined in this study, with slight injury to rice plants. The 2,6-dioxabicyclo[3,3,0]octane derivative, produced as a by-product, also showed high herbicidal activity.
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Novel 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2] benzopyran derivatives: synthesis of chiral glycol benzyl ether herbicides.
Pest management science, 2004Co-Authors: Takeshi Kakimoto, Fumiaki Koizumi, Kangetsu Hirase, Shinichi Banba, Eishi Tanaka, Kiyoshi AraiAbstract:Novel tricyclic 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran (TFB) derivatives were synthesized, and their herbicidal activities were elucidated. They were synthesized from D-glucose as a natural chiral source. The formation of the TFB skeleton was achieved by a Friedel-Crafts type intramolecular cyclization of methyl 5-deoxy-2,3-O-dibenzyl-5-C-methyl-D-xylofranosides. The intramolecular cyclization was dependent upon the electronic effects of the substituents at the C-2 Benzyloxy Group of methyl xylofranosides. Some TFBs exhibited a remarkable herbicidal activity to annual paddy weeds, such as Echinochloa sp, without injury to the rice.
Namakkal G. Ramesh - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of novel homoazanucleosides and their peptidyl analogs
Organic & biomolecular chemistry, 2020Co-Authors: Rahul Vilas Salunke, Pawan Kumar Mishra, Yogesh S. Sanghvi, Namakkal G. RameshAbstract:Synthesis of novel homoazanucleosides and their peptidyl analogs as hybrid molecules comprised of amino acids, an iminosugar and natural nucleobases is reported for the first time. A pluripotent amino-substituted chiral polyhydroxypyrrolidine, possessing orthogonally different functional Groups on either arm of the pyrrolidine ring, served as an ideal substrate for the synthesis of the proposed peptidyl homoazanucleosides. The acid sensitive primary Benzyloxy Group, on one arm of the pyrrolidine ring, after selective deprotection, was utilized for the introduction of nucleobases to obtain the homoazanucleosides. The amino Group on the other side offered the opportunity to be coupled with amino acids to deliver the desired peptidyl homoazanucleosides. Glycosidase inhibition studies revealed that the acetamido derivatives of homoazanucleosides were found to be sub-millimolar inhibitors of β-N-acetyl-glucosaminidase.
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A Concise Total Synthesis of the Stereoisomers of (–)‐Pochonicine
European Journal of Organic Chemistry, 2016Co-Authors: Rahul Vilas Salunke, Namakkal G. RameshAbstract:A concise total synthesis of the four stereoisomers of (–)-pochonicine was undertaken. The key steps of the synthesis involved chemoselective debenzylation of the primary Benzyloxy Group and an unprecedented Na–Hg-mediated concomitant N-detosylative intramolecular epoxide ring-opening reaction. Notably, additional steps for the protection of other functional Groups were not required. Glycosidase inhibition studies revealed that these compounds are inhibitors of β-N-acetylglucosaminidase with IC50 values in the sub-millimolar range.
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A Chiron Approach to Diversity-Oriented Synthesis of Aminocyclitols, (−)-Conduramine F‑4 and Polyhydroxyaminoazepanes from a Common Precursor
2016Co-Authors: Vimal Kant Harit, Namakkal G. RameshAbstract:The total syntheses of aminocyclitols, (−)-conduramine F-4, and polyhydroxyaminoazepanes have been achieved from a common precursor derived from tri-O-benzyl-d-glucal through a ‘diversity-oriented’ approach. Tri-O-benzyl-d-glucal was converted into a protected 1,6-diol through a sequence of steps that include transformation to a 2-tosylamidoglucose derivative, selective deprotection of primary C-6 Benzyloxy Group, LiAlH4-mediated one-step reduction of acetate Groups, and reductive ring opening of the resulting hemiacetal as the key steps. The 1,6-diol served as a common precursor in our diversity oriented approach toward the target molecules. Mesylation of the diol followed by double nucleophilic substitution reaction with primary amines led to the synthesis of amino-substituted polyhydroxyazepanes. On the other hand, dialdehyde obtained from the oxidation of 1,6-diol was found to be a convenient starting material for the synthesis of aminocyclitols and (−)-conduramine F-4. McMurry coupling of the dialdehyde was successfully employed, for the first time, to construct the carbocyclic framework of aminoyclitols, while bis-Wittig olefination of the dialdehyde followed by Grubb’s(II)-catalyzed RCM delivered (−)-conduramine F-4. The stereochemistry of newly created chiral centers in aminocyclitols was established through single crystal X-ray crystallography and detailed NOE studies
David Díaz Díaz - One of the best experts on this subject based on the ideXlab platform.
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[1,3]‐Transfer of Chirality during the Nicholas Reaction in γ‐Benzyloxy Propargylic Alcohols
Chemistry (Weinheim an der Bergstrasse Germany), 2006Co-Authors: David Díaz Díaz, Miguel A. Ramirez, Víctor S. MartínAbstract:A highly regio- and stereoselective intramolecular [1,5]-hydrogen-transfer process is described. Treatment of gamma-benzyl-protected Co2(CO)6-alpha,gamma-acetylenic diols with BF3 x OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether Group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the Benzyloxy Group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair-like transition state substantiated by a theoretical study is also included.
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Asymmetric synthesis of the (2S,4S,6S)-2,4,6-trimethylnonyl subunit of siphonarienes
Israel Journal of Chemistry, 2001Co-Authors: David Díaz Díaz, Fernando R. Pinacho Crisóstomo, Víctor S. MartínAbstract:The paper describes an asymmetric approach to the synthesis of the (2S,4S,6S)-2,4,6-trimethylnonyl segment of siphonarienes. The key step used is a newly developed methodology to obtain sec-dialkyl acetylenes based on theintramolecular hydride transfer from a secondary γ-Benzyloxy Group with well-defined absolute stereochemistry, ensured by a Sharpless asymmetric epoxidation reaction, to a cation generated by Lewis acid treatment of a tertiary Co 2 (CO) 6 -complexed propargylic alcohol.
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Enantioselective synthesis of alkyl-branched alkanes. Synthesis Of the stereoisomers of 7,11-dimethylheptadecane and 7-methylheptadecane, components of the pheromone of lambdina species
The Journal of organic chemistry, 2000Co-Authors: David Díaz Díaz, Víctor S. MartínAbstract:The stereoisomers of 7,11-dimethylheptadecane and 7-methylheptadecane have been synthesized. The key step used has been the intramolecular hydride transfer from a secondary gamma-Benzyloxy Group with defined absolute stereochemistry to a cation generated by Lewis acid treatment of the suitable tertiary Co(2)(CO)(6)-complexed propargylic alcohol. The application of this method provided stereochemically defined alpha-alkyl-gamma-hydroxy-acetylenes that after hydrogenation and further reductive elimination of the hydroxyl Group yielded sec-alkyl hydrocarbons.
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Enantiocontrolled synthesis of trialkyl-substituted stereogenic carbons. A general route to cis-3,5-dialkyl gamma-lactones
Organic letters, 2000Co-Authors: David Díaz Díaz, Víctor S. MartínAbstract:Lewis acid treatment of tertiary Co2(CO)6-propargylic alcohols having a stereochemically defined Benzyloxy Group at the γ-benzyl position yielded after cobalt demetalation sec-dialkyl bishomopropargylic alcohols in good yields. The reaction is highly stereoselective and predictable, providing pure stereoisomers. The use of benzyl-α,α‘-d2 ethers permitted the stereoselective d-labeling of methines and methylenes. Very simple chemical manipulations provided a general methodology to obtain the enantiomers of 3,5-dialkyl-γ-lactones.
Takeshi Kakimoto - One of the best experts on this subject based on the ideXlab platform.
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Novel glycol benzyl ether herbicides: Herbicidal activity of 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran derivatives
Journal of Pesticide Science, 2006Co-Authors: Takeshi Kakimoto, Fumiaki Koizumi, Kangetsu Hirase, Kiyoshi AraiAbstract:The structure–activity relationship of novel glycol benzyl ether herbicides, 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyrans (TFBs), was elucidated. Herbicidal activity against Echinochloa crus-galli and rice injury varied with substituents of the Benzyloxy Group at C-3. When substituents other than the Benzyloxy Group, such as the cyclohexylmethyloxy Group or the benzoyloxy Group, were introduced, the herbicidal activity of TFBs was reduced. Introduction of an (S)-methyl Group at C-5 increased herbicidal activity but aggravated rice injury. When comparing the herbicidal activity of two stereoisomers, the 5-(S)-isomer showed stronger herbicidal activity than the 5-(R)-isomer. Even when the benzene ring of the fused ring system of TFB was replaced by thiophene or furan, high herbicidal activity was manifested. In particular, TFB partly replaced by thiophene showed the highest herbicidal activity among all compounds examined in this study, with slight injury to rice plants. The 2,6-dioxabicyclo[3,3,0]octane derivative, produced as a by-product, also showed high herbicidal activity.
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Novel 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2] benzopyran derivatives: synthesis of chiral glycol benzyl ether herbicides.
Pest management science, 2004Co-Authors: Takeshi Kakimoto, Fumiaki Koizumi, Kangetsu Hirase, Shinichi Banba, Eishi Tanaka, Kiyoshi AraiAbstract:Novel tricyclic 3,3a,5,9b-tetrahydro-2H-furo[3,2-c][2]benzopyran (TFB) derivatives were synthesized, and their herbicidal activities were elucidated. They were synthesized from D-glucose as a natural chiral source. The formation of the TFB skeleton was achieved by a Friedel-Crafts type intramolecular cyclization of methyl 5-deoxy-2,3-O-dibenzyl-5-C-methyl-D-xylofranosides. The intramolecular cyclization was dependent upon the electronic effects of the substituents at the C-2 Benzyloxy Group of methyl xylofranosides. Some TFBs exhibited a remarkable herbicidal activity to annual paddy weeds, such as Echinochloa sp, without injury to the rice.