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The use of 4-methoxytrityl (monomethoxytrityl, Mmt) and 4-methyl-trityl (Mtt) groups of N1m-protection of Fmoc-His is described. Both groups being unaffected by base, e.g. piperidine and diethylamine, can be quantitatively removed under very mi
- Barlos, Kleomenis,Chatzi, Olga,Gatos, Dimitrios,Stavropoulos, George,Tsegenidis, Theodore
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- Base-induced rearrangement of tritylamines to imines: discovery and investigation of the mechanism
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An unexpected compound, the aniline derived benzophenone imine, was isolated when tritylamine was treated with n-BuLi and alkyl halides, during the formation of N-alkyl tritylamines, in the process of preparing primary amines. A nucleophilic attack of the nitrogen anion of tritylamide on the adjacent C-bonded phenyl, either substituted or not, involving a bridging anionic intermediate, is proposed for this base-induced tritylamine rearrangement to produce the corresponding imine. Electron-withdrawing groups in the aromatic ring, favoring the negative charge development, affect the relative migratory tendencies.
- Theodorou, Vassiliki,Skobridis, Konstantinos,Karkatsoulis, Aris
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p. 4284 - 4289
(2007/10/03)
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- A Kinetic Study of the Rearrangement of Triarylacetonitrile Oxides
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The thermal rearrangement of triphenylacetonitrile oxide (1a) to triphenylmethyl isocyanate (2) is a first-order process.Rate constants at five temperatures between 116 and 190 deg C were determined giving ΔH(excit.) = 9.3 +/- 1.1 kcal/mol and ΔS(excit.) = -58.2 +/- 2.4 cal/mol*K.The rearrangement of substituted triarylacetonitrile oxides (1b-d) occur only slightly faster than that of 1a.These results are interpreted in terms of a concerted single-step rearrangement in which the highly ordered transition state (6c) has a degree of radical character.
- Gibbs, Leslie W.,Wedegaertner, Donald K.
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p. 7320 - 7322
(2007/10/02)
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- Phenylvinylogously Extended Triphenylmethylium Systems
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As isoconjugated models for (phenylazo)tritylium ions of type A the tritylium systems containing one to three styryl or phenylethynyl substituents have been investigated.In accordance with simple theoretical model considerations these ions have VIS absorptions at considerably longer wavelengths than tritylium ion itself.They also show the expected bathochromic band shifts in going from the singly branched (1, 4) to the doubly and triply branched systems 2, 3 and 5, 6 as well as the predicted bathochromic shifts for 4-methoxystyryl (1b-3b) and hypsochromic shifts for 4-( dimethylammoniostyryl)- and 4-(nitrostyryl)tritylium ions 1c-3c and 1d, respectively.For most of the newly prepared tritylium systems fully resolved NMR spectra were obtained, whose signal positions correlate very well with the charge distributions derived from the elementary conjugation model.For the 4,4'-(1,2-ethenediyl)bistritylium system 12, whose color resembles that of 4-styryltritylium ion 1a, only the resonance lines of the inner protons 3,β-H and carbons C-4,β show significant deviations from the corresponding signal positions of the reference systems 1a and tritylium (13). - Key Words: Chromophores, combined / Ethene, diphenyl- / Ethyne, diphenyl- / Phenylmethylium
- Hellwinkel, Dieter,Fritsch, Helmut
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p. 2351 - 2360
(2007/10/02)
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