- Electrochemical synthesis of 1,2-diketones from alkynes under transition-metal-catalyst-free conditions
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We report an electrochemical protocol for the direct oxidation of internal alkynes in air to provide 1,2-diketones. A variety of functional groups and heterocycle-containing substrates can be tolerated well under mild conditions.
- Zhou, Jie,Tao, Xiang-Zhang,Dai, Jian-Jun,Li, Chen-Guang,Xu, Jun,Xu, Hong-Mei,Xu, Hua-Jian
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supporting information
p. 9208 - 9211
(2019/08/07)
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- New gas-phase domino processes leading to benzopyranones and benzofurans
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A new domino approach to flavones by gas phase pyrolysis of β,γ-dioxophosphonium ylides containing a 2-methoxyphenyl group is frustrated by unexpected and novel decarbonylation of the intermediate flavon-3-yl radical leading to 2-phenylbenzofuran. Alternative approaches based on dioxolane protection of one carbonyl, or selective elimination in β,β′-dioxo or β-oxo-β′-thioxo ylides were not successful, but pyrolysis of a β-oxo-β′-phenylimino ylide did give the required domino reaction leading to a protected benzopyranone in moderate yield.
- Aitken, R. Alan,Chang, Da
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p. 164 - 184
(2017/03/11)
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- Cycloaddition Reaction of Vinylphenylfurans and Dimethyl Acetylenedicarboxylate to [8 + 2] Isomers via Tandem [4 + 2]/Diradical Alkene-Alkene Coupling/[1,3]-H Shift Reactions: Experimental Exploration and DFT Understanding of Reaction Mechanisms
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An experimental test of designed [8 + 2] reaction of vinylphenylfuran and dimethyl acetylenedicarboxylate (DMAD) has been carried out, showing that the reaction gave unexpected addition products under different conditions. When the reaction was conducted under thermal conditions in toluene, expoxyphenanthrene, which was named as a [8 + 2] isomer, was generated. The scope of this reaction has been investigated in the present study. In addition, experiments and DFT calculations have been conducted to investigate how the reaction between vinylphenylfuran and DMAD took place. Surprisingly, the reaction did not involve the expected [8 + 2] intermediate, o-quinodimethane. Instead, the reaction starts from intermolecular Diels-Alder reactions between DMAD and the furan moiety of vinylphenylfuran, followed by unexpected intramolecular alkene-alkene coupling. This step generates a diradical species, which then undergoes [1,3]-H shift to give the experimentally observed expoxyphenanthrene. DFT calculations revealed that, the [8 + 2] cycloadduct cannot be obtained because the [1,5]-H shift process from the [1,5]-vinyl shift intermediate is disfavored kinetically compared to the [1,3]-H shift to the [8 + 2] isomer.
- Chen, Kai,Wu, Feng,Ye, Lijuan,Tian, Zi-You,Yu, Zhi-Xiang,Zhu, Shifa
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p. 8155 - 8168
(2016/09/28)
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- Lewis acid-catalyzed one-pot, three-component route to chiral 3,3′-bipyrroles
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(Chemical Equation Presented) 3,3′-Bipyrroles 3 could be synthesized using a double Michael addition reaction involving diaroyl acetylene 1 and the appropriate 1,3-dicarbonyls 2 using ammonium acetate as a nitrogen source. The axial chirality of bipyrrole was anticipated from the X-ray crystal structure and DFT calculations and confirmed by separating the racemates on a chiral column and subsequent CD spectra of the enantiomers. The absolute configuration of the enantiomers was achieved by theoretical CD spectra calculation using the ZINDO method.
- Dey, Sumit,Pal, Churala,Nandi, Debkumar,Giri, Venkatachalam Sesha,Zaidlewicz, Marek,Krzeminski, Marek,Smentek, Lidia,Hess Jr., B. Andes,Gawronski, Jacek,Kwit, Marcin,Babu, N. Jagadeesh,Nangia, Ashwini,Jaisankar, Parasuraman
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supporting information; experimental part
p. 1373 - 1376
(2009/04/10)
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- Catalysis by ionic liquid. A green protocol for the stereoselective debromination of vicinal-dibromides by [pmIm]BF4 under microwave irradiation
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An easily accessible ionic liquid, 1-methyl-3-pentylimidazolium fluoroborate, [pmIm]BF4, has been demonstrated to be an efficient catalyst as well as reaction medium for the stereoselective debromination of a variety of structurally diverse vicinal-dibromides to the corresponding (E)-alkenes in high yields under microwave irradiation. This reaction does not require any organic solvent and any metal or any conventional reducing agent, and the ionic liquid is recycled without any appreciable loss of its catalytic efficiency.
- Ranu, Brindaban C.,Jana, Ranjan
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p. 8621 - 8624
(2007/10/03)
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- Selective oxidation of acetylenic 1,4-diols with dioxiranes in comparison with the methyltrioxorhenium-hydrogen peroxide oxidant
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Dimethyldioxirane (DMD) and its trifluoro analog (TFD) were employed to achieve selectively the direct transformation of diol 3a and of diol 3b into the corresponding carbonyls. The results are compared with oxidations using methyltrioxorhenium (MTO)/85%
- D'Accolti, Lucia,Fiorentino, Michele,Fusco, Caterina,Crupi, Pasquale,Curci, Ruggero
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p. 8575 - 8578
(2007/10/03)
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- Cycloaddition of thiophene S-oxides to allenes, alkynes and to benzyne
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Thiophenes have been treated with alkynes in the presence of m-chloroperoxybenzoic acid to give substituted arenes as cycloadducts. Alternatively, thiophene S-oxides have been prepared by oxidation from thiophenes and have been subjected to cycloaddition with alkynes in a subsequent step. The outcome of the reaction is dependent on the steric demand of the thiophene S-oxide. Some thiophene S-oxides can be reacted at temperatures as high as 140°C without decomposition. Thiophenes as deoxygenated products are the main by-products. Reactions of thiophene S-oxides with allenes give in part thiabicyclo[2.2.1]heptene S-oxides of type 12a and 13 along with aromatized products. Thiophene S-oxides also cycloadd to benzyne.
- Thiemann, Thies,Fujii, Hideki,Ohira, Daisuke,Arima, Kazuya,Li, Yuanqiang,Mataka, Shuntaro
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p. 1377 - 1384
(2007/10/03)
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- Flash Vacuum Pyrolysis of Stabilized Phosphorous Ylides. Part 5. Selective Extrusion of Ph3PO from β,γ,β'-Trioxo Ylides to give Doacylalkynes
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Sixteen examples of the previously unknown trioxo ylides 7 have been prepared by acylation of stabilized phosphorus ylides 8 with α-oxo acid chlorides 9.Extrusion of Ph3PO from these is readily achieved using FVP at 500 deg C in most cases, to afford the diacylalkynes 10 in moderate yield.Three examples failed to give the expected alkynes and the nature of the processes involved in these cases is certain.Fully assigned 13C NMR spectra are presented for the ylides and an unexpected pattern is observed in the value of JP-C for the three carbonyl carbons depending on the nature of the substituents present.There is some correlation between the value of 2JP-C for the central carbonyl carbon and the success of the pyrolysis although this is not complete.The method has been used to prepare a specifically 13C labelled acetylenic diester 14.
- Aitken, R. Alan,Herion, Hugues,Janosi, Amaya,Karodia, Nazira,Raut, Swati V.,et al.
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p. 2467 - 2472
(2007/10/02)
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- Pyrolysis of β,γ,β'-trioxo phosphorus ylides: Convenient synthesis of symmetrical and unsymmetrical diacylalkynes
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Flash vacuum pyrolysis of a series of 1,2,4-trioxo-3-triphenylphosphoranylidene-butane derivatives, formed by acylation of β-oxo-phosphorus ylides with α-oxo-acid chlorides, results in extrusion of Ph3PO exclusively across the 2,3-position to give diacylalkynes.
- Aitken,Herion,Janosi,Raut,Seth,Shannon,Smith
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p. 5621 - 5622
(2007/10/02)
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- ANODIC OXIDATION OF DIARYLACETYLENES AND DIARYLDIACETYLENES: ELECTROSYNTHESIS OF DIAROYL-STILBENES AND ACETYLENIC α- AND γ-DIKETONES
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Diarylacetylenes and diaryldiacetylenes have been electrooxidized in acetonitrile through the use of a graphite plate anode, thus overcoming a very high passivation.Diarylacetylenes led mainly to 1,2-diaroyl-1,2-diaryl-ethylenes.Anodic oxidation of conjugated diaryldiacetylenes, at the same anode, led to a mixture of acetylenic α- and γ-diketones.This represents the very first synthesis of acetylenic α-diketones Ar-CO-CO-CC-Ar.
- Cariou, Michel
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p. 799 - 808
(2007/10/02)
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- Electro-oxidation of Diarylacetylenes and Diaryldiacetylenes
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Diarylacetylenes led to 1,2-diaroyl-1,2-diarylethylenes and diaryldiacetylenes led to a mixture of acetylenic α- and γ-diketones, by anodic oxydation in MeCN-LiClO4 on a graphite plate electrode.
- Cariou, Michel,Simonet, Jacques
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p. 445 - 446
(2007/10/02)
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- Ylidions: A New Reactive Intermediate Prepared by Photosensitized One-Electron Oxidation of Phenacyl Sulfonium Ylides
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The chemistry of a series of phenacyl sulfonium ylides was studied.Their photosensitized one-electron oxidation by 9,10-dicyanoanthracene generates ylidions, a new class of radical cation intermediates.In some cases, the ylidions cleave to form a free alkyl radical and a cation; in others, they are attacked by nucleophiles or by an alkene.The chemical properties displayed by the phenacyl sulfonium ylidions appear to be controlled primarily by the nature of the sulfur-bound alkyl groups.The direct photolysis and thermolysis of the phenacyl sulfonium ylides was examined for comparison with their one-electron oxidation.Some of the ylides undergo the Stevens rearrangement either when heated or photolyzed.Contrary to an earlier report, there is no evidence that direct photolysis of a phenacyl sulfonium ylide leads to formation of benzoylcarbene.
- Zhang, Jian-Jian,Schuster, Gary B.
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p. 7149 - 7155
(2007/10/02)
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- Photochemical Transformations and Laser Flash Photolysis Studies of 1,4- and 1,2-Epoxy Compounds Containing 1,2-Dibenzoylalkene Moieties
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Photochemical transformations of a few 1,4- and 1,2-epoxy ketones have been investigated.Irradiation of a benzene solution of 1 gave a mixture of 3 (32percent) and dibenzoylacetylene (DBA, 6, 13percent), whereas the photolysis of 8 in methanol gave a mixture of the ester 12 (56percent) and DBA (22percent).Irradiation of 14 in benzene gave a mixture of the isomeric lactone 17 (25percent), 1,3-diphenylisobenzofuran (20, 20percent), and o-dibenzoylbenzene (23, 10percent).The photolysis of 24 in both benzene and methanol resulted in isomerization to the anthracene derivative 25 (6percent and 20percent).The same product (25, 38percent) was obtained in the thermolysis of 24.Plausible mechanisms for the formation of the various products have been discussed.Laser flash photolysis (337.1 nm) of 1, 8, and 14 in benzene and methanol led to the observation of short-lived transient species, characterized by absorption maxima at 405-490 nm and by lifetimes (τT) in the range 0.4-2.0 μs.Pulse-radiolytic observation of the same transients under energy-transfer sensitization as well as detailed quenching studies using oxygen, di-tert-butylnitroxide, azulene, ferrocene, and β-carotene led to the assignments of the transients as triplets.The quantum yields of triplet formation (ΦT) under direct laser excitation were estimated to be high (0.50-0.74).Upon laser flash photolysis, 24 produced the anthracene derivative 25 nearly within the laser pulse; the intermediacy of a triplet with τT ca.7 ns and ΦT ca.1 was established in this case by quenching studies involving 1-methylnaphthalene and 2,5-dimethyl-2,4-hexadiene.
- Murty, B. A. R. C.,Kumar, C. V.,Dabral, V.,Das, P. K.,George, M. V.
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p. 4165 - 4171
(2007/10/02)
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