- CIDNP and CIDEP Studies on Intramolecular Hydrogen Abstraction Reaction of Polymethylene-Linked Xanthone and Xanthene. Determination of the Exchange Integral of the Intermediate Biradicals
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Hydrogen abstraction reaction of a polymethylene-linked system is investigated by using chemically induced dynamic nuclear and electron polarization (CIDNP and CIDEP) methods.The reaction scheme is determined from the CIDNP and CIDEP spectra of the unlinked xanthene and xanthone system.The exchange integral J between the two terminal radicals of the system is obtained from the simulation process by using the spin-correlated CIDEP theory modified with (a) the fast population relaxation between the central S-T0 mixed states, (b) the contribution from the triplet mechanism, and (c) hyperfine line dependent line width.The mechanism of the fast population relaxation and the dependence of the J value on the temperature and polymethylene chain length are discussed.
- Maeda, Kiminori,Terazima, Masahide,Azumi, Tohru,Tanimoto, Yoshifumi
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Read Online
- Synthesis of xanthones, thioxanthones and Acridones by a metal-free photocatalytic oxidation using visible light and molecular oxygen
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9H-Xanthenes, 9H-thioxanthenes and 9,10-dihydroacridines can be easily oxidized to the corresponding xanthones, thioxanthones and acridones, respectively, by a simple photo-oxidation procedure carried out using molecular oxygen as oxidant under the irradiation of visible blue light and in the presence of riboflavin tetraacetate as a metal-free photocatalyst. The obtained yields are high or quantitative.
- Chinchilla, Rafael,Torregrosa-Chinillach, Alejandro
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- Oxidation of alcohols and activated alkanes with lewis acid-activated tempo
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The reactivity of MCl3(η1O) (M = Fe, 1; Al, 2; TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) with a variety of alcohols, including 3,4-dimethoxybenzyl alcohol, 1-phenyl-2-phenoxyethanol, and 1,2-diphenyl-2-methoxyethanol, was investigated using NMR spectroscopy and mass spectrometry. Complex 1 was effective in cleanly converting these substrates to the corresponding aldehyde or ketone. Complex 2 was also able to oxidize these substrates; however, in a few instances the products of overoxidation were also observed. Oxidation of activated alkanes, such as xanthene, by 1 or 2 suggests that the reactions proceed via an initial 1-electron concerted proton-electron transfer (CPET) event. Finally, reaction of TEMPO with FeBr3 in Et2O results in the formation of a mixture of FeBr3(η1OH) (23) and [FeBr2(η1OH)]2(μ-O) (24), via oxidation of the solvent, Et2O.
- Nguyen, Thuy-Ai D.,Wright, Ashley M.,Page, Joshua S.,Wu, Guang,Hayton, Trevor W.
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p. 11377 - 11387
(2015/02/19)
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- Synergistic effect of ketone and hydroperoxide in Bronsted acid catalyzed oxidative coupling reactions
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Waste not wasted: A mechanistic study of the autoxidative coupling of xanthene with cyclopentanone uncovered an autoinductive effect of the waste product hydrogen peroxide. It generates radicals in the presence of acid and ketones, which accelerate the reaction by providing an additional pathway to the reactive hydroperoxide intermediate. This discovery could be applied to achieve other Bronsted acid catalyzed oxidative coupling reactions.
- Schweitzer-Chaput, Bertrand,Sud, Abhishek,Pinter, Aron,Dehn, Stefanie,Schulze, Philipp,Klussmann, Martin
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supporting information
p. 13228 - 13232
(2014/01/06)
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- A high-valent iron-oxo corrolazine activates C-H bonds via hydrogen-atom transfer
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Oxidation of the FeIII complex (TBP8Cz)Fe III [TBP8Cz = octakis(4-tert-butylphenyl)corrolazinate] with O-atom transfer oxidants under a variety of conditions gives the reactive high-valent Fe(O) complex (TBP8Cz+?)Fe IV(O) (2). The solution state structure of 2 was characterized by XAS [d(Fe-O) = 1.64 A]. This complex is competent to oxidize a range of C-H substrates. Product analyses and kinetic data show that these reactions occur via rate-determining hydrogen-atom transfer (HAT), with a linear correlation for log k versus BDE(C-H), and the following activation parameters for xanthene (Xn) substrate: ΔH? = 12.7 ± 0.8 kcal mol -1, ΔS? = -9 ± 3 cal K-1 mol-1, and KIE = 5.7. Rebound hydroxylation versus radical dimerization for Xn is favored by lowering the reaction temperature. These findings provide insights into the factors that control the intrinsic reactivity of Compound I heme analogues.
- Cho, Kevin,Leeladee, Pannee,McGown, Amanda J.,Debeer, Serena,Goldberg, David P.
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experimental part
p. 7392 - 7399
(2012/06/16)
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- Oxidation of C-H bonds by [(bpy)2(py)RuIVO] 2+ occurs by hydrogen atom abstraction
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Anaerobic oxidations of 9,10-dihydroanthracene (DHA), xanthene, and fluorene by [(bpy)2(py)RuIVO]2+ in acetonitrile solution give mixtures of products including oxygenated and non-oxygenated compounds. The products include those formed by organic radical dimerization, such as 9,9′-bixanthene, as well as by oxygen-atom transfer (e.g., xanthone). The kinetics of these reactions have been measured. The kinetic isotope effect for oxidation of DHA vs DHA-d4 gives k H/kD ≥ 35 ± 1. The data indicate a mechanism of initial hydrogen-atom abstraction forming radicals that dimerize, disproportionate and are trapped by the oxidant. This mechanism also appears to apply to the oxidations of toluene, ethylbenzene, cumene, indene, and cyclohexene. The rate constants for H-atom abstraction from these substrates correlate well with the strength of the C-H bond that is cleaved. Rate constants for abstraction from DHA and toluene also correlate with those for oxygen radicals and other oxidants. The rate constant for H-atom transfer from toluene to [(bpy)2(py)RuIVO]2+ appears to be close to that predicted by the Marcus cross relation, using a tentative rate constant for hydrogen atom self-exchange between [(bpy)2(py)Ru IIIOH]2+ and [(bpy)2(py)RuIVO] 2+.
- Bryant, Jasmine R.,Mayer, James M.
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p. 10351 - 10361
(2007/10/03)
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- Reactions of Carbanions with two Sterically Demanding 1-Benzoylaziridines: SET, SN2, Carbonyl Attack.
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Reactions of 2-phenyl (1a) and 2-benzyl (1b) 1-benzoyl-2-butylaziridines with carbanions X-, AH-, and Fl- of xanthene, dihydroanthracene and fluorene always form N-(2-butylethyl)-benzamides carrying phenyl (9a) or benzyl (9b).This reductive ring opening indicates an SET mechanism with aziridino ketyls 6a,b as intermediates.Nucleophilic ring opening (SNs) is found only with the carbanion of the lowest reducing power: Fl- 5a,b (62percent, 14percent).These two mechanisms cleave different bonds, a finding without precedence in SN2/SET competitions.Carbonyl addition resulting in benzoyl transfer to xanthene, dihydroanthracene or fluorene is usually also observed.It is the main reaction with X- and 1a.The highest yields of 9a,b are obtained with AH- since a special inner-sphere SET is available.
- Bellos, Konstantinos,Stamm, Helmut
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p. 269 - 273
(2007/10/02)
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- Single Electron Transfer versus Nucleophilic Ring Opening in Reactions of Cis-Trans Pairs of Activated 2-Phenylaziridines. Strong Influence of Nitrogen Pyramid for N-Benzoylaziridines
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Activated 2-phenylaziridines with a second substituent R in position 3 were made to react with xanthyl anion X(1-).Nucleophilic ring opening is the only reaction that occurs with sulfonyl activation.The analogous N-benzoylaziridines 1 undergo this type of ring opening when the two substituents Ph and R are trans.The cis isomers (cis-1, Ph and R cis) react in this manner to a negligible extent if any.The (nearly) exclusive ring cleavage reaction of cis-1 is C-N homolysis of an intermediate ketyl formed by single electron transfer (SET) from X(1-).This cis-trans phenomenon is in accordance with the hypothesis that the two competing reactions depend in an opposite manner on the steepness of the nitrogen pyramid.A predominant or exclusive final result of SET is reductive aziridine opening and dimerization of the xanthyl radical X(.).Formation of both diastereomers of the amidoethylated xanthene in one case (R = Me) is evidence for a cross combination of X(.) with the radical formed by homolytic ring opening.Cross combination is also a likely path for R = H (no cis-trans isomerism), in addition to reductive ring opening. cis-Aziridines with dimethylcarbamoyl on nitrogen do not react via SET since the ketyl is not stabilized and therefore difficult to generate.Carbonyl attack on both types of acylaziridines competes more or less successfully with the two ring cleavage reactions.
- Falkenstein, Reinhard,Mall, Thomas,Speth, Dieter,Stamm, Helmut
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p. 7377 - 7381
(2007/10/02)
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- Mechanism of Photoisomerization of Xanthene to 6H-Dibenzopyran in Aqueous Solution
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A new photoreaction, the photoisomerization of xanthene (1) to 6H-dibenzopyran (2) (ca. 70percent) (Φ = 0.0035 in 7:3 H2O-CH3CN) in aqueous CH3CN solution is reported.In addition to 2, 2-benzylphenol (3) (Φ ca. 0.001), 9,9'-bixanthyl (4) (Φ 1, to generate a singlet biradical.Trivial recombination gives back unreacted 1.Hydrogen abstraction from solvent leads to the photoreduction product 3.However, recombination of the biradical at the ipso benzylic position (ortho to phenol) gives a cyclohexadienone intermediate 17.Subsequent transformation of this species to 2 occurs via an o-quinone methide intermediate 18, which itself can be trapped with MeOH or H2O, to give the corresponding methyl ether derivative 8 or alcohol 5.
- Huang, C.-G.,Shukla, Deepak,Wan, Peter
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p. 5437 - 5442
(2007/10/02)
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- N-S Cleavage Is Faster Than Homolytic Ring Opening in Single-Electron Transfer to Some N-Sulfonylaziridines. Competition between SN2 and SET
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The radical anions of the N-sulfonylaziridines, 1a,b and 3 undergo N-S cleavage in place of homolytic ring opening as is demonstrated by reactions with anthracenide A*-.Nucleophilic ring opening of the sulfonylaziridines 1a,b and 3 by the carbanions AH-, X-, and Fl- of dihydroanthracene, xanthene, and fluorene, respectively, proceeds with the expected regioselectivity and is slow enough to allow some competition by a single-electron transfer (SET) initiated N-S cleavage, which provides the desulfonated aziridines and bixanthenyl X-X or bifluorenyl Fl-Fl, respectively.The SET path is favored by light.The competition is in favor of SET to the exclusion of the nucleophilic opening when trityl anion reacts with 1a.The twice-found byproducts 11 and 12 require the azirine intermediate 15, which is, at least formally, generated by elimination of TsH from 1a in a non-SET reaction.
- Bellos, Konstantinos,Stamm, Helmut,Speth, Dieter
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p. 6846 - 6849
(2007/10/02)
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- Arene Hydrides, 8. - SET vs. Nucleophilic Attack in Reactions of α-Bromoisobutyrophenone with Carbanions. Fragmentation of the Anion of Tetrahydrobianthracene
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SET is the main reaction pathway between α-bromoisobutyrophenone (1) and the carbanions 7a-j- of diarylmethanes or disubstituted acetonitriles: 7- 7. + e and e + 1 Br- PhCOCMe2. (3).Main secon
- Werry, Juergen,Stamm, Helmut,Sommer, Andreas
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p. 1553 - 1562
(2007/10/02)
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- Novel reductive couplinog-rearrangement of carbonyl compounds with metal/Lewis acid under irradiation of ultrasonic wave
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Novel reductive coupling-rearrangement of carbonyl compounds such as benzophenones with Al or Zn/ AlCl3 in CH3CN under irradiation of ultrasonic wave gave benzopinacolones via epoxides in good yields.
- Sato, Ryu,Nagaoka, Takeshi,Saito, Minoru
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p. 4165 - 4168
(2007/10/02)
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- Organosulfur Compounds, L. - 2H-Thiopyrans and Dihydro-2H-thiopyrans, Synthons for Thiophenes
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2H-Thiopyran derivatives yield thiophenes on pyrolysis at 240-260 deg C.The influence of substitution in positions 3 to 6 of the 2H-thiopyrans on these new thermal rearrangement and fragmentation reactions is dealt with, and some proposed mechanisms are discussed in detail.A novel three-step synthesis of thiophenes from carbonyl compounds via the corresponding thiones, their -cycloaddition with 1,3-dienes with formation of dihydro-2H-thiopyrans and subsequent thermal conversion is described.In this reaction sequence, whose scope and limitations are outlined, t he thiocarbonyl compound contributes the sulfur and the 1,3-diene the carbon skeleton of the desired thiophenes.
- Praefcke, Klaus,Weichsel, Christian
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p. 1604 - 1619
(2007/10/02)
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- Example of false OSAR prediction: About spasmolytic xanthenyl-mandelates
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The tertiary and quaternary 2-diethylaminoethyl xanthenylmandelates were synthesized and tested for spasmolytic activity on the guinea-pig isolated ileum. The quaternary ester 2 acts as a poor competitive antagonist at the muscarinic receptor. Its affinit
- Lambrecht,Moser,Mutschler
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p. 305 - 310
(2007/10/02)
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- New Olefin and Oxiran Syntheses from Carbonyl Compounds, and Diethyl Sodiophosphonate Anions and 1-Aminophosphonate Amino-anions
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Reaction of aromatic aldehydes, and phthalic and thiophthalic anhydrides, with diethyl sodiophosphonate (1) gives the trans-stilbenes (3), 3,3'-biphthalidylidene (30), and 3,3'-bis-(2-thiophthalidylidene) (33).Similar treatment of fluorenone (8) and xanthone (17) with (1) leads to 9,9'-bis(fluororenylidene) (9) and 9,10-dihydro-9-oxophenanthrene-10-spiro-9'-fluorene (10), and to 9,9'-bixanthenylidene (18) and 9,9'-bixanthenyl (19), respectively, but the reaction using anthrone (11) as a carbonyl reagent yields only anthraquinone (12) and anthracene (13).Similar treatment using N-methylisatoic anhydride (34) and N-methylisatin (36) produces NN'-dimethylisoindigo (35).Reaction of benzaldehyde and p-chlorobenzaldehyde with diethyl 1--cyclohexylphosphonate (40) gives mainly corresponding mixtures of trans- (41a,b) and cis-stilbene epoxides (42a,b), while similar treatment of p-nitrobenzaldehyde with (40) produces 4,4'-dinitrostilbene (3e).Reaction of (8) with (40), as well as with (1), gives (9) and (10).The mechanism of formation of these products is discussed.
- Minami, Toru,Matsuzaki, Narihide,Ohshiro, Yoshiki,Agawa, Toshio
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p. 1731 - 1738
(2007/10/02)
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