- Synthesis and Photodimerization of 2- And 2,3-Disubstituted Anthracenes: Influence of Steric Interactions and London Dispersion on Diastereoselectivity
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There is increased evidence that the effect of bulky groups in organic, organometallic, and inorganic chemistry is not only repulsive but can be attractive because of London dispersion interactions. The influence of the size of primary alkyl substituents in 2- and 2,3-positions of anthracenes on the diastereoselectivity (anti vs syn dimer) of the [π4s + π4s] photoinduced dimerization is investigated. The synthesis of the anthracene derivatives was achieved by Suzuki-Miyaura reaction of 2,3-dibromoanthracene with alkylboronic acids as well as by reduction of anthraquinones that were obtained from 2,3-disubstituted 1,3-butadienes and naphthoquinone followed by dehydrogenation. The mixtures of dianthracene isomers were analyzed with respect to the anti/syn-ratio of the products by X-ray crystallography and nuclear Overhauser effect spectroscopy. While for the 2,3-dimethylanthracene the anti and syn isomers were formed in equal amounts, the anti dimers are the major products in all other cases. A linear correlation (R2 = 0.98) between the steric size (Charton parameter) and the isomeric ratio suggests that the selectivity is dominated by classical repulsive steric effects. An exception is the iso-butyl substituent that produces an increased amount of the syn isomer. It is suggested that this is due to an exalted effect of London dispersion interactions.
- Geiger, Thomas,Haupt, Anne,Maichle-M?ssmer, C?cilia,Schrenk, Claudio,Schnepf, Andreas,Bettinger, Holger F.
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p. 10120 - 10135
(2019/08/26)
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- Bromination of aromatic compounds using an Fe2O 3/zeolite catalyst
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The catalytic bromination of non-activated aromatic compounds has been achieved using an Fe2O3/zeolite catalyst system. FeBr 3 was identified as the catalytic species, formed in situ from HBr and Fe2O3. The catalyst was easy-to-handle and cost effective and could also be recycled. The reaction system was also amenable to the one-pot sequential bromination/C-C bond formation of benzene.
- Nishina, Yuta,Takami, Keishi
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supporting information
p. 2380 - 2383
(2013/02/21)
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- Brominated methanes as photoresponsive molecular storage of elemental Br2
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The photochemical generation of elemental Br2 from brominated methanes is reported. Br2 was generated by the vaporization of carbon oxides and HBr through oxidative photodecomposition of brominated methanes under a 20 W low-pressure mercury lamp, wherein the amount and situations of Br2 generation were photochemically controllable. Liquid CH 2Br2 can be used not only as an organic solvent but also for the photoresponsive molecular storage of Br2, which is of great technical benefit in a variety of organic syntheses and in materials science. By taking advantage of the in situ generation of Br2 from the organic solvent itself, many organobromine compounds were synthesized in high practical yields with or without the addition of a catalyst. Herein, Br2 that was generated by the photodecomposition of CH2Br2 retained its reactivity in solution to undergo essentially the same reactions as those that were carried out with solutions of Br2 dissolved in CH 2Br2 that were prepared without photoirradiation. Furthermore, HBr, which was generated during the course of the photodecomposition of CH2Br2, was also available for the substitution of the OH group for the Br group and for the preparation of the HBr salts of amines. Furthermore, the photochemical generation of Br2 from CH2Br2 was available for the area-selective photochemical bleaching of natural colored plants, such as red rose petals, wherein Br2 that was generated photochemically from CH 2Br2 was painted onto the petal to cause radical oxidations of the chromophoric anthocyanin molecules. The generation of Br 2 from brominated methanes occurred upon photoirradiation under O2. The solutions that contained elemental Br2 were useful for the synthesis of organobromine compounds and the macroscopic photochemical bleaching of colored plants. Copyright
- Kawakami, Kazumitsu,Tsuda, Akihiko
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p. 2240 - 2252
(2012/11/06)
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- Evidence for fully conjugated double-stranded cycles
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A chain of circumstantial evidence for the existence of the first fully conjugated, double-stranded cycles is presented. The products have the structure of the belt-region of fullerene C84 (D2) and carry either four hexyl chains or four phenyl groups. The unsubstituted parent cycle is also presented. The chain of evidence is mainly based on mass spectrometric analysis and trapping reactions, the latter being supported by quantum mechanical calculations. It is also of importance that the phenyl-substituted and unsubstituted products cannot undergo a [1,5] hydrogen shift, the only reasonable side-reaction that recently could not be excluded for the alkyl-substituted analogue. It is concluded that the fully aromatic targets truly exist in the gas phase. Whether they can be generated in solution under the applied conditions cannot yet be firmly decided; theoretical evidence speaks against.
- Standera, Malte,Haefliger, Rolf,Gershoni-Poranne, Renana,Stanger, Amnon,Jeschke, Gunnar,Van Beek, Jacco D.,Bertschi, Louis,Schlueter, A. Dieter
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supporting information; experimental part
p. 12163 - 12174
(2011/11/14)
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- Cross coupling of polybromoiodobenzenes with some terminal alkynes
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Sonogashira reactions of pentabromoiodobenzene and tetrabromo-1,4- diiodobenzene with various terminal alkynes at 20°C in benzene resulted in selective replacement of the iodine atoms with formation of the corresponding alk-1-yn-1-yl-substituted polybromobenzenes.
- Shishkin,Tarasova,Khlevin
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experimental part
p. 1323 - 1326
(2009/07/17)
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- Regioselectivity of reductive debromination of substituted pentabromobenzenes with sodium tert-butoxide in DMSO
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The regioselectivity of reductive debromination of substituted pentabromobenzenes C6Br5X (X = NH2, OMe, Me, H, Cl, F, and NO2) under the action of ButONa in DMSO containing ButOH has been studied. The reaction followed the halophilic mechanism via carbanions.
- Shishkin,Tarasova,Butin
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p. 2379 - 2383
(2007/10/03)
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- IPTYCENES EXTENDED TRIPTYCENES
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Triptycene is the first member of a large scale of compounds for which we have coined the general term "iptycenes".The prefix (tri, pent, etc.) indicates the number of separated arene planes.By fusing from one to six 9,10-anthradiyl moieties on the triptycene framework, one can derive a first generation of iptycenes (Table 1).Of these, only 3, 4, 8 and a substituted 2 are known; the remainder provide a synthetic challenge.Potentially interesting practical and theorethical properties of iptycenes and particular structural features of several (i.e. 15, 16 and 24) arebriefly discussed, as are certain extensions beyond the compounds in Table 1.Methods for preparing useful synthons 35-41 are described.Three new, much improved syntheses of triptycene 29, itself a useful iptycene synthon, are presented.In addition, improved syntheses of pentiptycenes 3 and 33 are described, as well as the first syntheses of pentiptycenes 32, 34 and 52 and heptiptycene 54.The way is paved for future development of this mini-domain of unnatural products.
- Hart, Harold,Bashir-Hashemi, Abdollah,Luo, Jihmei,Meador, Mary Ann
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p. 1641 - 1654
(2007/10/02)
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- THE DILITHIATION MECHANISM IN THE REACTIONS OF POLYHALOARENES AS DI-ARYNE EQUIVALENTS
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The preparation of certain 1,4-dilithio-tetrahaloarenes is described; they react with electrophiles at low temperatures or form arynes at higher temperatures.
- Hart, Harold,Nwokogu, Godson C.
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p. 5721 - 5724
(2007/10/02)
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