- Tris(1-naphthyl)- and tris(2-naphthyl)methyl cations: Highly crowded triarylmethyl cations
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The highly hindered tris(1-naphthyl)methyl and tris(2-naphthyl)methyl cations 3 and 5 have been prepared under long lived stable ion conditions and characterized by 13C NMR spectroscopy at low temperatures. The latter can abstract hydride from cycloheptatriene to afford tris(2-naphthyl)methane 7, but the reaction of cycloheptatriene with the more crowded cation 3 failed to give the corresponding hydrocarbon. A primary kinetic isotope effect, kH/kD = 7.1 ± 0.5, found in the former case supports a colinear hydride abstraction mechanism. The ions 3 and 5 upon quenching rearranged to give a mixture of isomeric 13-(1-naphthyl)-1,2,7,8-dibenzofluorene 4 and 13-(2-naphthyl)-2,3,6,7-dibenzofluorene 6, respectively.
- Olah, George A.,Liao, Qimu,Casanova,Bau, Robert,Rasul, Golam,Prakash, G. K. Surya
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- Optimized synthesis and detailed NMR spectroscopic characterization of the 1,8a-dihydroazulene-1,1-dicarbonitrile photoswitch
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An economical and effective protocol for large scale synthesis of the 2-phenyl-1,8adihydroazulene-1,1-dicarbonitrile (DHA) photoswitch has been developed. This compound is ring-opened by light to a vinylheptafulvene (VHF), which is thermally closed back to DHA. This compound serves as an important starting material for dihydroazulene photoswitches incorporating a substituent in the seven-membered ring and as a reference compound for comparison of properties. A detailed NMR spectroscopic characterization has allowed the assignment of all proton and carbon signals. In addition, the compound was characterized by Xray crystallography. A correlation between the rate constant for thermal ring-closure of VHF to DHA and empirical parameters of solvent polarity (ET (30)) was established. ARKAT-USA, Inc.
- Broman, Soren Lindbaek,Brand, Sophie Lehn,Parker, Christian Richard,Petersen, Michael Axman,Tortzen, Christian Gregers,Kadziola, Anders,Kilsa, Kristine,Nielsen, Mogens Brondsted
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experimental part
p. 51 - 67
(2011/06/19)
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- Synthesis and Isolation of Polytrityl Cations by Utilizing Hexaphenylbenzene and Tetraphenylmethane Scaffolds
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The successful isolation of stable (and soluble) hexa- and tetratrityl cations based on hexaphenyl-benzene and tetraphenylmethane scaffold has been accomplished by using readily available starting materials. These robust polytrityl cations can be isolated in crystalline form and stored indefinitely at 0 °C. Their structures have been established by 1H/ 13C NMR spectroscopy and by UV-vis spectroscopy. The structures of these polytrityl cations were further confirmed by quantitative transformations to the reduced (poly)triphenylmethyl derivatives by hydride transfer from triethylsilane, cycloheptatriene, or a borane-dimethyl sulfide complex.
- Rathore, Rajendra,Burns, Carrie L.,Guzei, Ilia A.
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p. 1524 - 1530
(2007/10/03)
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- Mode attack of atomic carbon on benzene rings
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Reaction of are generated carbon atoms with tert-butylbenzene, 4, gives 3-methyl-3-phenyl-1-butene, 5, and 1,1-dimethylindane, 6. Labeling studies and isotope effects demonstrate that 5 results from an insertion into a methyl C-H bond followed by 1,2 hydrogen shift while 6 arises from initial ortho C-H insertion followed by intramolecular insertion into a methyl C-H bend. When fluoroboric acid is added to the 77 K matrix of 4 + C, tert-butyltropylium fluoroborate, 18, is formed. Labeling studies indicate that 18 results from initial insertion of C into meta and para C-H bonds of 4 followed by ring expansion to cycloheptatetraenes which are subsequently protonated. The reaction of C with benzene gives similar results, indicating that initial C-H insertion is the preferred mode of attack of atomic carbon on benzene rings.
- Armstrong, Brian M.
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p. 6007 - 6011
(2007/10/03)
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- Cyclisation reactions of 2-substituted biphenyl-2'-yldiazonium salts leading to O-alkyldibenzofuranium and S-alkyldibenzothiophenium salts: Modified Meerwein reagents
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The preparation of 2-amino-2'-methoxybiphenyl and 2-amino-2'-thiomethoxybiphenyl and analogues and their transformation into diazonium salts and hence into dibenzofuranium and dibenzothiophenium salts is described together with their use as alkylating agents.
- Downie,Heaney,Kemp,King,Wosley
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p. 4005 - 4016
(2007/10/02)
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- Anodic oxidation of cycloheptatriene systems and its application to the synthesis of non-benzenoid aromatic compounds
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Anodic oxidation of cycloheptatrienes has been found to be one of the most powerful key tools for the preparation of a variety of non-benzenoid aromatic compounds such as tropylium salts, tropones, tropolones, 2H-cyclohepta[b]furan-2-ones, and azulenes.
- Shono, Tatsuya,Nozoe, Tetsuo,Maekawa, Hirofumi,Yamaguchi, Yoshihide,Kanetaka, Shinya,Masuda, Haruhisa,Okada, Toshio,Kashimura, Shigenori
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p. 593 - 603
(2007/10/02)
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- ANODIC TRANSFORMATION OF CYCLOHEPTATRIENE TO TROPONE AND TROPOLONE
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Cycloheptatriene (CHT) has been directly transformed to 7-methoxycycloheptatriene (7-MCHT), an equivalent compound to a tropolium salt, by the anodic oxidation of CHT in methanol.The further anodic oxidation of 3-MCHT prepared from 7-MCHT has been found to be an effective method of synthesis of tropone and tropolone.
- Shono, Tatsuya,Nozoe, Tetsuo,Maekawa, Hirofumi,Kashimura, Shigenori
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p. 555 - 558
(2007/10/02)
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- Reactions of 1,3-Dithiolan-2-ylium and 1,3-Dithian-2-ylium Tetrafluoroborates and Ambident 2-Styryl Derivatives
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The ambident 2-styryl-1,3-dithiolan-2-ylium and 2-styryl-1,3-dithian-2-ylium cations react with preferential carbon-carbon bond formation at the β ethylenic carbon when treated with methylmagnesium iodide.In the lithium aluminium hydride reaction, reduction occurs at either electrophilic carbon center.Methanol and thiophenol react selectively with the β carbon of the side chain.The adduct formation with the heteroatom nucleophiles is readily reversed by acid catalysis.In the absence of the styryl group, the nucleophilic addition is at C-2.Dithioketals of symmetric 1,2-divarbonyl derivatives are readily formed by zinc-induced reductive dimerization of 1,3-dithiolan- and 1,3-dithian-2-ylium salts.
- Klaveness, Jo,Rise, Frode,Undheim, Kjell
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p. 373 - 380
(2007/10/02)
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- 1,3-Dithienium- and 1,3-Dithiolenium Salts, V. Determination of the Relative Reactivity of 1,3-Dithian-2-ylium Tetrafluoroborates by Intermolecular Hydride Ion Transfer
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The 1,3-dithienium- and 1,3-dithiolenium tetrafluoroborates 4 (n=3, 2) react in good yields with the (trimethylsiloxy)alkenes 3 available from β-dicarbonyl compounds to give the 2-substituted 1,3-dicarbonyl compounds 5.Owing to the formation of the difluoroboron acid esters 8 as competition products 3 has to be employed in excess, however.Reaction of 4 (n=3) with 1,3,5-cycloheptatriene (10) leads to the 1,3-dithianes 11 and the more stable tropylium tetrafluoroborate (12).The determination of the corresponding rates of reduction allows in a simple manner the ascertainment of the relative reactivities of 4.Whereas the reactivities of the aryl-substituted representatives of 4 show a sufficient correlation corresponding to the Hammett relationship, the variations of the reactivities of the alkyl substituted salts 4 can be explained on the basis of hyperconjugative stabilization.
- Stahl, Ingfried
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p. 4857 - 4868
(2007/10/02)
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- CARBON-CARBON BOND FORMATION BY COORDINATION OF CARBOCATIONS WITH CARBANIONS.
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Direct attack of resonance-stabilized carbenium ions and carbanions can be regulated to provide a wide range of rates and equilibria for the study of carbon-carbon bond formation.
- Arnett, Edward M.,Troughton, E. B.
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p. 3299 - 3302
(2007/10/02)
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- Regiospecific Synthesis of 1,2-Dialkylthio-7(alkyl-or aryl)thiocycloheptatrienes and 1,2-Dialkylthio-7-alkoxycycloheptatrienes
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Hydride abstraction by trityl tetrafluoborate from a mixture of cycloheptatriene- and cycloheptatriene-p-dithiine gave tropenylium-p-dithiin tetrafluoborate.The latter was found to add either methoxide or various thiolates only at the tropenylium C-3, which constitutes the first entry to regiospecifically trifunctionalized cycloheptatrienes.In contrast, cycloheptatriene-p-dithiine or various other cycloheptatrienes substituted at C-7 with either methylthio or t-butylthio groups were found to undergo alkylthiolate abstraction by trityl tetrafluoborate.This limits the usefulness of the above synthetic methods for polyfunctionalized cycloheptatrienes. - Keywords: Tropenylidenes, Tropenylium Ions, Hydride Abstraction
- Cavazza, Marino,Morganti, Gioia,Pietra, Francesco
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p. 786 - 788
(2007/10/02)
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