- Full Cleavage of C≡C Bond in Electron-Deficient Alkynes via Reaction with Ethylenediamine
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Reaction of 1,2-diaminioethane (ethylenediamine) with electron-deficient alkynes leads to full scission of the C≡C bond even in the absence of a keto group directly attached to the alkyne. This process involves oxidation of one of the alkyne carbons into C2 of a 2-R-4,5-dihydroimidazole with the concomitant reduction of the other carbon to a methyl group. The sequence of Sonogashira coupling with the ethylenediamine-mediated fragmentation described in this work can be used for selective formal substitution of halogen in aryl halides by a methyl group or a 4,5-dihydroimidazol-2-yl moiety.
- Vasilevsky, Sergei F.,Davydova, Maria P.,Mamatyuk, Victor I.,Tsvetkov, Nikolay,Hughes, Audrey,Baranov, Denis S.,Alabugin, Igor V.
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p. 421 - 429
(2017/04/07)
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- The Rearrangement of Aromatic Compounds. Part 3. The Mechanism of Rearrangement of Nitrated Hydrocarbons in Trifluoromethanesulphonic Acid
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1,3-Dialkyl-2-nitrobenzenes (C6H3R2NO2; R = Me, Et, and Pri) rearrange in trifluoromethanesulphonic acid to the corresponding 4-nitro derivatives; with R = Et, this reaction is accompanied by dehydration to 7-ethyl-3-methylanthranil.The reaction rate increases markedly with the size of the alkyl group; with R = Me, the reaction was studied at 110 deg C but, with R = Pri, temperatures of 36-54 deg C were used.The studies with R = Me show the reaction to be first-order with the rate coefficients (k1) increasing rapidly with the acidity of the solution 1)/d(-H0)> = 1.45, decreasing with acidity to o.49.Double-labelling experiments with 1H and 15N show the reaction to be intramolecular. 1,2,4-Trimethyl-3-nitrobenzene also rearranges under these conditions to give mainly the 5-nitro isomer.The above results are discussed in terms of a direct 1,3-shift of the nitro group.
- Bullen, John V.,Ridd, John H.,Sabek, Omaima
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p. 1681 - 1685
(2007/10/02)
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- 4. Synthese von Plectranthonen, diterpenoiden Phenanthren-1,4-chinonen
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The following phenanthrene-1,4-diones have been synthesized by using the photocyclization of the corresponding highly substituted stilbenes as the key step: 3-hydroxy-5,7,8-trimethyl-2-(prop-2-enyl)phenanthrene-1,4-dione (1), (RS)-, (R)-, and (S)-2--1-methylethyl)acetate (2, 31, and 32, resp.), 3-hydroxy-7,8-dimethyl-2-(prop-2-enyl)phenanthrene-1,4-dione (3), 3-hydroxy-7,8,10-trimethyl-2-(prop-2-enyl)phenanthrene-1,4-dione (4), 5,7,8-trimethyl-2-(prop-2-enyl)phenanthrene-1,4-dione (17) and 3-hydroxy-2-methylphenanthrene-1,4-dione (42).The quinones 1 and 3 proved to be identical with recently isolated plectranthons A and C.Compounds 2, 31, and 32 exhibited the same UV/VIS, IR, 1H-NMR and mass spectra as natural plectranthon B, but had different melting points.This might be due either to crystal modifications or to diastereoisomerism caused by the helical structure of the phenanthrene-1,4-dione skeleton.The spectral data of synthetic 4 were not compatible with those of natural plectranthon D for which structure 4 had been proposed based mainly on 1H-NMR arguments concerning the chemical shifts of H-C(9) and H-C(10) in 1-3.Extensive 1H-NMR investigations have now revealed that the currently stated assignments of the H-C(9)/H-C(10) AB system have to be reversed for highly substituted phenanthrene-1,4-diones: in the model compounds 2-methylphenanthrene-1,4-dione (41) and 2, H-C(10) resonates at lower field as expected (peri-position), whereas in the highly substituted congeners 1, 2, 3, 31, and 32, H-C(9) is shifted paramagnetically, a fact which had lead to the erroneous assignment of structure 4 for natural plectranthon D.
- Kaliakoudas, Dimitrios,Eugster, Conrad Hans,Rueedi, Peter
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- Aromatic Substitution. 48. Boron Trifluoride Catalyzed Nitration of Aromatics with Silver Nitrate in Acetonitrile Solution
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Benzene, alkylbenzenes, halobenzenes, and anisole were nitrated with silver nitrate/boron trifluoride in acetonitrile solution.Correlation of competitive rates with ?- and ?-complex stabilities indicated that the transition state of highest energy lies relatively early on the reaction coordinate.Data indicate that nitrations occur via a polarized complex of the nitrating agent, with the catalyst undergoing nucleophilic displacement by the aromatic substrate.
- Olah, George A.,Fung, Alexander P.,Narang, Subhash C.,Olah, Judith A.
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p. 3533 - 3537
(2007/10/02)
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- Aromatic Substitution. 471. Acid-Catalyzed Transfer Nitration of Aromatics with N-Nitropyrazole, a Convenient New Nitrating Agent
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N-Nitropyrazole in the presence of Lewis or Bronsted acid catalysts was found to be an effective transfer nitrating agent for aromatic substrates.The nature of the acid catalyst both substrate and positional selectivies of the nitration of alkylbenzenes.No relationship was found between substrate and positional selectivities, which are considered to be determined in two separate steps.
- Olah, George A.,Narang, Subhash C.,Fung, Alexander P.
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p. 2706 - 2709
(2007/10/02)
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