Search results for "Carbocation"
showing 7 items of 17 documents
Reaktionen von elektronenreichen Heterocyclen mit Orthocarbonsäure-Derivaten, 10. Formylierungs- und Alkylierungsreaktionen von Carbazolen mit ambide…
1987
Carbazole werden durch Diethoxycarbenium-tetrafluoroborat mit hoher Regioselektivitat formyliert, wahrend die thermodynamisch stabileren Diethoxymethylcarbenium- und Trimethoxycarbenium-Ionen infolge ausgepragter ambidenter Elektrophilie Carbazole bevorzugt alkylieren. Reactions of Electron-Rich Heterocycles with Orthocarboxylic Acid Derivatives, 10. – Formylation and Alkylation of Carbazoles with Ambident Dialkoxycarbenium Tetrafluoroborates Carbazole and some derivatives were formylated regioselectively with diethoxycarbenium tetrafluoroborate. The thermodynamically more stable diethoxymethylcarbenium and trimethoxycarbenium ions exhibit ambident electrophilic reactivity as predominant al…
Tris[oligo(1,4-phenylenevinylene)]methylium Dyes
2009
The tris[oligo(1,4-phenylenevinylene)]carbinols 2a–f (n =1–4) and the tris(4-styrylphenyl)methanes 7a,b have been prepared by Wittig–Horner (3 + 4a–f 2a–f) and Siegristreactions (5 + 6a,b 7a,b). The Wittig–Horner reactions in these examples are accompanied by an autoxidation, whereas a reduction occurs in the Siegrist reactions. Compound 2a, the lowest member (n = 1) of the series 2a–d with terminal dialkylamino groups, generates first, on treatment with acids, the methylium dye 2′a, which absorbs far into the NIR region (λmax = 1100 nm). The higher members 2b,c (n = 2,3) of the carbinol series yield by acidic treatment only N-protonated methylium dyes 2″′b,c. The different behavior is due …
Tris(2-thienyl)methyl cation; An unprecedent 13C NMR behavior
1986
Abstract An unexpected response of the chemical shift value to the substitution of phenyl by thienyl groups is found in the series 1–8 . On this basis the planar cation 7 appears to show an homoaromatic-like peripheral ring current.
Configuration of Enolates of β-Ketocarboxylic Acid Esters — Carbocation-Carbanion Salts
1996
Deprotonation of (Z)- or (E)-3-hydroxy-2,3-dimesitylpropenoic acid methyl ester (1a) with tetrakis(dimethylamino)-methane (3) led to stable salt (E)-2a, which belongs to a very rare species of salts that consist of a heteroatom-stabilized carbocation and a heteroatom-stabilized carbanion. An analogous guanidinium salt (E)-2b was formed in the reaction of 3-oxo-2,3-diphenylpropanoic acid methyl ester (1b) and 3. The molecular structures of these enolates were studied by NMR spectroscopy and an X-ray analysis of (E)-2a {MC[N(CH3)2]3} and compared with those of the corresponding alkali enolates.
ISomerization of xylene: MINDO/3 study of the cyclization of benzenium cation into bicyclo[3.1.0]hexenyl cation
1989
Abstract A MINDO/3 study of thermal electrocyclic closing of the benzenium cation to form a bicyclo[3.1.0]hexenyl cation is presented. The calculated mechanism discusses the possibility of cyclization of xylenium cations on a silica catalyst or in superacid media. The structure and energy of the transition state, the enthalpies of isomerization and barriers of activation were calculated for the following processes: isomerization of 2,6-dimethylbenzenium cation into 2,6-dimethylbicyclo[3.1.0]hexenyl cation, isomerization of 2,4-dimethylbenzenium cation into 2,4-dimethylbicyclo[3.1.0]-hexenyl cation, and isomerization of benzenium cation into bicyclo[3.1.0]-hexenyl cation. Equilibrium and kin…
Reaktivitäut und reaktionswege von methylsubstituierten bisindolylcarbenium-ionen
1987
Methyl substituted bisindolylcarbenium ions 1 react with some O- and C-nucleophiles regioselectively. The cations 1b, 1c yield with hydroxide ions the tetraindolyldimethyl ether 4 and with methoxide ions the bisin-dolylmethoxymethanes 5. Compounds 1a, 1b, 1c react with several methylindoles to isomeric bis- and trisin-dolylmethanes. An electrophilic reactivity order of cations 1 can be derived supporting on the experimental results.
Water compatible gold(III)-catalysed synthesis of unsymmetrical ethers from alcohols.
2008
An efficient and broad-scoped method for the preparation of unsymmetrical ethers from alcohols catalysed by the simplest and least expensive gold catalyst, NaAuCl 4 , is described for the first time. The procedure enables the etherification of benzylic and tertiary alcohols with moderate to good yields under mild conditions with low catalyst loading. Symmetrical ethers, the usual side products in the etherification of alcohols, were not detected in this case. The formation of the racemic ether from a chiral benzyl alcohol suggests the intermediacy of a carbocation, which has not previously been postulated for gold-catalysed reactions involving alcohols.