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Hiroshi Yamataka - One of the best experts on this subject based on the ideXlab platform.
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Dynamic path bifurcation in the Beckmann Reaction: support from kinetic analyses.
The Journal of organic chemistry, 2011Co-Authors: Yutaro Yamamoto, Hiroto Hasegawa, Hiroshi YamatakaAbstract:The Reactions of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles when the migrating groups have reasonable stability as cations. The Reactions of oxime sulfonates of 1-substituted-phenyl-2-propanone derivatives (7-X) and related substrates (8-X, 9a-X) in aqueous CH3CN gave both rearrangement products (amides) and fragmentation products (alcohols), the ratio of which depends on the system; the Reactions of 7-X gave amides predominantly, whereas 9a-X yielded alcohols as the major product. The logk–logk plots between the systems gave excellent linear correlations with slopes of near unity. The results support the occurrence of path bifurcation after the rate-determining TS of the Beckmann rearrangement/fragmentation Reaction, which has previously been proposed on the basis of molecular dynamics simulations. It was concluded that path-bifurcation phenomenon could be more common than thought and that a reactivity-selectivity argument based on the...
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Dynamic path bifurcation for the Beckmann Reaction: observation and implication
Faraday Discuss., 2010Co-Authors: Hiroshi Yamataka, Makoto Sato, Hiroto Hasegawa, Salai Cheettu AmmalAbstract:The Reaction of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles instead of amides when the cations have reasonable stability. The Reactions of oxime derivatives of 1-substituted-phenyl-2-propanones and 3-substituted-phenyl-2-butanones in aqueous solvents gave both rearrangement and fragmentation products, the ratio of which was dependent on substituents. Transition state (TS) optimizations and intrinsic Reaction coordinate (IRC) calculations for the Reaction of 1-phenyl-2-propanone oximes showed that there is a single TS for each substituted compound. The IRC path from the TS either led to a rearrangement product or a fragmentation product depending on the substituent; the IRC path changes from rearrangement to fragmentation when substituent X becomes more electron donating. Ab initio dynamics simulations were found to follow the IRC path for X = p-NH2 and p-MeO giving fragmentation products, and almost so for X = p-NO2 giving the rearrangement products. However, in a borderline case where X is less donating than p-MeO or less withdrawing than p-NO2, the trajectories did not follow the minimum energy path on the potential energy surface, but gave both rearrangement and fragmentation products directly from the single TS. This is a novel example of path bifurcation for a closed shell anionic Reaction. It was concluded that a reactivity-selectivity argument based on the traditional TS theory may not always be applicable even to a well-known textbook organic Reaction.
Kovuru Gopalaiah - One of the best experts on this subject based on the ideXlab platform.
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Oxalic acid:A very useful bronsted acid in organic synthesis
Synlett, 2004Co-Authors: Kovuru GopalaiahAbstract:(A) Oxalic acid is an efficient reagent for the Beckmann Reaction - a variety of ketoximes are converted into the corresponding secondary amides by classical anti-periplanar migration upon heating to ca. 100 °C, and aldoximes afford the corresponding nitriles. The procedure offers high yield of the desired products, gaseous byproducts $(CO + CO_2)$ and the absence of Reaction solvent. (B) Anhyd. oxalic acid is an excellent mediator for one-pot transformation of ketones to amides in the presence of hydroxylamine hydrochloride. The method is effective for various arom. and aliph. ketones, and provides excellent yield of the products. (C) In the presence of aq. oxalic acid, enol ethers undergo expeditious hydrolysis to the corresponding ketones without concomitant migration of the double bond. In contrast, use of a mineral acid typically gives the conjugated ketone. This method offers considerable advantage in terms of regioselectivity of the product.
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Beckmann Reaction of oximes catalysed by chloral: mild and neutral procedures
Tetrahedron Letters, 2003Co-Authors: Sosale Chandrasekhar, Kovuru GopalaiahAbstract:A variety of ketoximes undergo the Beckmann rearrangement when heated with 0.5 molar equiv. of chloral (neat melt/1\sim30°C), to furnish the corresponding amides in excellent yields (generally 80–95%) after simple work-up. (Aromatic aldoximes dehydrated to the corresponding nitriles in excellent yields under similar conditions.) The absence of solvent, Bronsted acids, strong Lewis acids and by-products, and a simple work-up characterise the procedures.
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Beckmann rearrangement of ketoximes on solid metaboric acid: a simple and effective procedure
Tetrahedron Letters, 2002Co-Authors: Sosale Chandrasekhar, Kovuru GopalaiahAbstract:When ketoximes admixed with solid metaboric acid (formed from boric acid at 100degreesC/0.1 Torr) are heated (similar to 140degreesC/7-42 h), the corresponding amides or lactams are produced in excellent yields (62-92%) via the Beckmann Reaction. Aromatic aldoximes undergo both dehydration to the nitrile as well as (non-stereospecific) rearrangement under the above conditions. The absence of solvent, and the mildness and low toxicity of boric acid, characterise the present procedure. CO. 2002 Elsevier Science Ltd. All rights reserved.
Hiroto Hasegawa - One of the best experts on this subject based on the ideXlab platform.
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Dynamic path bifurcation in the Beckmann Reaction: support from kinetic analyses.
The Journal of organic chemistry, 2011Co-Authors: Yutaro Yamamoto, Hiroto Hasegawa, Hiroshi YamatakaAbstract:The Reactions of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles when the migrating groups have reasonable stability as cations. The Reactions of oxime sulfonates of 1-substituted-phenyl-2-propanone derivatives (7-X) and related substrates (8-X, 9a-X) in aqueous CH3CN gave both rearrangement products (amides) and fragmentation products (alcohols), the ratio of which depends on the system; the Reactions of 7-X gave amides predominantly, whereas 9a-X yielded alcohols as the major product. The logk–logk plots between the systems gave excellent linear correlations with slopes of near unity. The results support the occurrence of path bifurcation after the rate-determining TS of the Beckmann rearrangement/fragmentation Reaction, which has previously been proposed on the basis of molecular dynamics simulations. It was concluded that path-bifurcation phenomenon could be more common than thought and that a reactivity-selectivity argument based on the...
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Dynamic path bifurcation for the Beckmann Reaction: observation and implication
Faraday Discuss., 2010Co-Authors: Hiroshi Yamataka, Makoto Sato, Hiroto Hasegawa, Salai Cheettu AmmalAbstract:The Reaction of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles instead of amides when the cations have reasonable stability. The Reactions of oxime derivatives of 1-substituted-phenyl-2-propanones and 3-substituted-phenyl-2-butanones in aqueous solvents gave both rearrangement and fragmentation products, the ratio of which was dependent on substituents. Transition state (TS) optimizations and intrinsic Reaction coordinate (IRC) calculations for the Reaction of 1-phenyl-2-propanone oximes showed that there is a single TS for each substituted compound. The IRC path from the TS either led to a rearrangement product or a fragmentation product depending on the substituent; the IRC path changes from rearrangement to fragmentation when substituent X becomes more electron donating. Ab initio dynamics simulations were found to follow the IRC path for X = p-NH2 and p-MeO giving fragmentation products, and almost so for X = p-NO2 giving the rearrangement products. However, in a borderline case where X is less donating than p-MeO or less withdrawing than p-NO2, the trajectories did not follow the minimum energy path on the potential energy surface, but gave both rearrangement and fragmentation products directly from the single TS. This is a novel example of path bifurcation for a closed shell anionic Reaction. It was concluded that a reactivity-selectivity argument based on the traditional TS theory may not always be applicable even to a well-known textbook organic Reaction.
Salai Cheettu Ammal - One of the best experts on this subject based on the ideXlab platform.
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Dynamic path bifurcation for the Beckmann Reaction: observation and implication
Faraday Discuss., 2010Co-Authors: Hiroshi Yamataka, Makoto Sato, Hiroto Hasegawa, Salai Cheettu AmmalAbstract:The Reaction of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles instead of amides when the cations have reasonable stability. The Reactions of oxime derivatives of 1-substituted-phenyl-2-propanones and 3-substituted-phenyl-2-butanones in aqueous solvents gave both rearrangement and fragmentation products, the ratio of which was dependent on substituents. Transition state (TS) optimizations and intrinsic Reaction coordinate (IRC) calculations for the Reaction of 1-phenyl-2-propanone oximes showed that there is a single TS for each substituted compound. The IRC path from the TS either led to a rearrangement product or a fragmentation product depending on the substituent; the IRC path changes from rearrangement to fragmentation when substituent X becomes more electron donating. Ab initio dynamics simulations were found to follow the IRC path for X = p-NH2 and p-MeO giving fragmentation products, and almost so for X = p-NO2 giving the rearrangement products. However, in a borderline case where X is less donating than p-MeO or less withdrawing than p-NO2, the trajectories did not follow the minimum energy path on the potential energy surface, but gave both rearrangement and fragmentation products directly from the single TS. This is a novel example of path bifurcation for a closed shell anionic Reaction. It was concluded that a reactivity-selectivity argument based on the traditional TS theory may not always be applicable even to a well-known textbook organic Reaction.
Yutaro Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Dynamic path bifurcation in the Beckmann Reaction: support from kinetic analyses.
The Journal of organic chemistry, 2011Co-Authors: Yutaro Yamamoto, Hiroto Hasegawa, Hiroshi YamatakaAbstract:The Reactions of oximes to amides, known as the Beckmann rearrangement, may undergo fragmentation to form carbocations + nitriles when the migrating groups have reasonable stability as cations. The Reactions of oxime sulfonates of 1-substituted-phenyl-2-propanone derivatives (7-X) and related substrates (8-X, 9a-X) in aqueous CH3CN gave both rearrangement products (amides) and fragmentation products (alcohols), the ratio of which depends on the system; the Reactions of 7-X gave amides predominantly, whereas 9a-X yielded alcohols as the major product. The logk–logk plots between the systems gave excellent linear correlations with slopes of near unity. The results support the occurrence of path bifurcation after the rate-determining TS of the Beckmann rearrangement/fragmentation Reaction, which has previously been proposed on the basis of molecular dynamics simulations. It was concluded that path-bifurcation phenomenon could be more common than thought and that a reactivity-selectivity argument based on the...