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338 results on '"Hasegawa, Eietsu"'

3. Desulfonylative Radical Truce–Smiles Rearrangement Utilizing the Benzimidazoline and Benzimidazolium Redox Couple.

Author

Miyajima, Ryo, Okamura, Manon, Oomori, Kazuki, Iwamoto, Hajime, Wakamatsu, Kan, and Hasegawa, Eietsu

Subjects
RADICALS (Chemistry), OXIDATION-reduction reaction, ABSTRACTION reactions, CHEMICAL reactions, CHEMICAL processes, NAD (Coenzyme)
Abstract

This article explores the use of benzimidazoline and benzimidazolium redox couples in the desulfonylative radical Truce-Smiles rearrangement. The authors investigate the reactivity of these compounds and their potential applications in various chemical processes. They also examine the factors that affect the yield of the rearrangement reactions and propose optimal conditions for carrying out the conversion. The study provides insights into the use of these redox couples as promoters in radical reactions. Additionally, the authors develop a photocatalytic system using benzimidazolines as electron and hydrogen atom donors, with picoline borane as a catalyst. The study includes density functional theory calculations to gain insight into the intermediates involved in the reaction pathway. The results of this research have implications for organic synthesis, photochemistry, electron transfer chemistry, and radical chemistry. [Extracted from the article]

Published
2024
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22. Photoreactions of 4-(tribromomethyl)-4-methyl-2,5-cyclohexadienone and its derivatives with amines: radical cyclization and ring expansion reactions promoted through photoinduced electron transfer processes

Author

Hasegawa, Eietsu, Tamura, Yukinobu, Suzuki, Kimiko, Yoneoka, Akira, and Suzuki, Toshio

Subjects
Chemistry, Organic -- Research, Amines -- Research, Ring formation (Chemistry) -- Research, Oxidation-reduction reaction -- Research, Biological sciences, Chemistry
Abstract

A study of the photoinduced electron transfer (PET) reactions of 4-(tribromomethyl)-4-methyl-2,5-cyclohexadienone and its derivatives with different amines is examined. The effects of added water, solvents and amine structure on the product ratio have been discussed.

Published
1999

24. Electron-transfer reaction of aromatic alpha,beta-epoxy ketones: factors that govern selective conversion to beta-diketones and beta-hydroxy ketones

Author

Hasegawa, Eietsu, Ishiyama, Kenyuki, Fujita, Takayuki, Kato, Tomoyasu, and Abe, Toshiaki

Subjects
Ketones -- Analysis, Aromatic compounds -- Analysis, Epoxy compounds -- Analysis, Oxidation-reduction reaction -- Analysis, Biological sciences, Chemistry
Abstract

Beta-diketones and beta-hydroxy ketones were formed by the irradiation of trans-4'-cyanochalcone epoxide with amines. The synthetic process that led to the formation of the beta-hydroxy ketone involved an amine cation radical-assisted beta-hydrogen abstraction from the ring-opened form of the epoxy ketone anion radical. The effective formation of beta-hydroxy ketone was also dependent on the proton-donating ability of the amine cation radical and the timing of proton transfer to the anionic intermediates.

Published
1997

25. Photochemically and thermally induced free-radical reactions of alpha,beta-epoxy ketones with tributyltin hydride: selective C(sub alpha)-O bond cleavage of oxiranylmethyl radicals derived from alpha,beta-epoxy ketones

Author

Hasegawa, Eietsu, Ishiyama, Kenyuki, Kato, Tomoyasu, Horaguchi, Takaaki, Shimizu, Takahachi, Tanaka, Shoji, and Yamashita, Yoshiro

Subjects
Free radical reactions -- Research, Photochemistry -- Methods, Epoxy compounds -- Research, Ketones -- Research, Ethylene oxide -- Research, Tributyltin -- Research, Biological sciences, Chemistry
Abstract

alpha,beta-Epoxy ketones undergo free-radical photochemicaland thermal reactions with tributyltin hydride (TBTH) to yield beta-hydroxy ketones. The thermal process is initiated by azoisobutyronitrile while the photoreaction starts with H-atom abstraction of the ketone triplet from TBTH. Both processes involve a TBTH radical attack on the carbonyl followed by regioselective opening of the oxiranylmethyl ring. Trapping of the free- radical intermediate provides evidence for a unique 1,5-tributyltin transfer. Epoxy esters and alcohols, on the other hand, do not undergo such ring- openingreactions.

Published
1992

29. Cyclization and ring-expansion processes involving samarium diiodide promoted reductive formation and subsequent oxidative ring opening of cyclopropanol derivatives

Author

Tsuchida, Hiroyuki, Tamura, Mutsuko, and Hasegawa, Eietsu

Subjects
Cyclopropane compounds -- Chemical properties, Cyclopropane compounds -- Structure, Ring-opening polymerization -- Analysis, Samarium -- Chemical properties, Samarium -- Structure, Biological sciences, Chemistry
Abstract

Samarium diiodide promoted reaction of various [alpha]-bromomethyl cycloalkanones, followed by subsequent treatment with trimethylsilyl chloride, which leads to the production of cyclopropyl silyl ethers embedded in bicyclo[m.1.0]alkane frameworks is described. The regioselectivities of cyclopropane ring opening in the bicyclic substrates is found to depend on the oxidizing agents used.

Published
2009

48. A Unique and Simple Preparative Method for α-Arylpipecolinic Acid Esters via Base-induced Sommelet-Hauser Rearrangement

Author

Tayama, Eiji, Sato, Ryota, Ito, Motoshi, Iwamoto, Hajime, Hasegawa, Eietsu, Tayama, Eiji, Sato, Ryota, Ito, Motoshi, Iwamoto, Hajime, and Hasegawa, Eietsu

Abstract

A unique and simple preparative method for N-cyano--aryl pipecolinic acid esters via base-induced Sommelet–Hauser rearrangement, the von Broun reaction, and intramolecular -alkylation is reported. The removal of the N-cyano substituent was achieved by hydrogenation and hydride reduction.

Published
2013

49. AN EFFECTIVE PROCEDURE TO PROMOTE AZA-PRINS CYCLIZATION REACTIONS EMPLOYING A COMBINATION OF FERRIC CHLORIDE AND AN IMIDAZOLIUM SALT IN BENZOTRIFLUORIDE

Author

Osawa, Chika, Tateyama, Minami, Miura, Kensuke, Tayama, Eiji, Iwamoto, Hajime, Hasegawa, Eietsu, Osawa, Chika, Tateyama, Minami, Miura, Kensuke, Tayama, Eiji, Iwamoto, Hajime, and Hasegawa, Eietsu

Abstract

Aza–Prins cyclization reactions of N-tosyl-3-butenylamine with p-methoxybenzaldehyde, 1-naphthaldehyde and 2-naphthaldehyde take place efficiently using a combination of ferric chloride and 1-butyl-3-methylimidazolium hexafluorophosphate in benzotrifluoride (FeIm–BTF procedure). The new methodology, leading to formation of target N-tosyl-4-chloro-2-substituted piperidines, is superior to the one using 1-butyl-3-methylimidazolium tetrachloroferrate. The FeIm–BTF procedure was also applied to aza–Prins cyclization reactions of other aldehydes. Finally, the effects of imidazolium salts on aza–Prins cyclization reaction promoted by boranetrifluoride-diethyl ether complex, leading to formation of fluorinated piperidines, were explored.

Published
2012

50. Copper(II)–acid co-catalyzed intermolecular substitution of electron-rich aromatics with diazoesters

Author

Tayama, Eiji, Ishikawa, Moe, Iwamoto, Hajime, Hasegawa, Eietsu, Tayama, Eiji, Ishikawa, Moe, Iwamoto, Hajime, and Hasegawa, Eietsu

Abstract

The intermolecular aromatic substitution of N,N-dialkylanilines and alkoxybenzenes with diazoesters is shown to proceed in the presence of catalytic amounts of both copper(II) salt and acid (Lewis or Brønsted). This method is a mild and rare metal-free C–C bond formation reaction between aromatic (sp2) and aliphatic (sp3) carbons.

Published
2012

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