- UNEXPECTED REGIOSELECTIVE DIELS-ALDER CYCLOADDITION REACTIONS BETWEEN 3-FLUOROBENZYNE AND 2-ALKYLFURANS
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The Diels-Alder reaction between 3-fluorobenzyne (1) and 2-alkylfurans (2) gives a mixture of syn adduct 3 and anti adduct 4.The syn cycloadduct invariably predominates and the regioselectivity increases in the order: R= Me Et i-Pr t-Bu, to a maximum of 90percent syn adduct 3d for 2-tert-butylfuran.These results are rationalized in terms of a concerted nonsynchronous transition state that reflects an alkyl steric effect and a polarized aryne 1.
- Gribble, Gordon W.,Keavy, Daniel J.,Branz, Stephen E.,Kelly, William J.,Pals, Mark A.
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- Nickel complex catalyzed efficient activation of sp3and sp 2c-h bonds for alkylation and arylation of oxygen containing heterocyclic molecules
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A nickel(II) complex (1) of N,N'-bis(2,6-diisopropylphenyl)-2,6- pyridinedicarboxamido (L) ligand was examined for catalytic coupling of Grignard reagents with the C-H bond of oxygen containing heterocyclic compounds such as tetrahydrofuran and furan. The nickel( II) complex showed excellent activity in catalyzing C-H activation and further coupling with various Grignard reagents. The effective activation of the C-H bond proceeded under ambient reaction conditions with a short reaction time (1-2 h). The catalyst (1) displays high turnover frequency of 4,130 h-1with catalyst loading as low as 0.01 mol%. This catalytic route could prove to be an efficient mode of activation of sp3and sp2C-H bonds in various heterocycles for the preparation of synthetically and pharmaceutically relevant molecules. Springer Science+Business Media New York 2013.
- Gartia, Yashraj,Ramidi, Punnamchandar,Jones, Darin E.,Pulla, Sharon,Ghosh, Anindya
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p. 507 - 515
(2014/06/24)
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- Activation of sp3 and sp2 C-H bonds of oxygen containing heterocyclic molecules for alkylation and arylation reactions catalyzed by an iron complex
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Activation of both sp3 and sp2 CH bonds is reported using an efficient iron(III) complex (1) of a ligand (N2,N6-bis(2,6- diisopropylphenyl)pyridine-2,6-dicarboxamide: L). The iron(III) complex showed catalytic activity of CC coupling reaction of oxygen containing heterocycles, e.g. tetrahydrofuran (THF), with various alkyl, allyl and aryl Grignard reagents under ambient reaction conditions. Complex 1 demonstrated excellent activity and reactions were completed within 30 min to 1 h. A high turnover frequency (TOF) of 1700 h-1 using a low catalyst loading of 0.02 mol% was obtained for the reaction. Interestingly, the catalyst was selective in activation of the CH bond adjacent to the oxygen in various oxygen containing heterocyclic molecules to yield 2-substitituted products.
- Gartia, Yashraj,Ramidi, Punnamchandar,Cheerla, Sreevishnu,Felton, Charlette M.,Jones, Darin E.,Das, Bhaskar C.,Ghosh, Anindya
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p. 253 - 259
(2014/07/07)
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- PtII-catalyzed hydrophenylation of α-olefins: Variation of linear/branched products as a function of ligand donor ability
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The PtII complexes [(xbpy)Pt(Ph)(THF)]+ (xbpy = 4,4′-X2-2,2′-bipyridyl; x = OMe (1a), tBu (1b), H (1c), Br (1d), CO2Et (1e) and NO2 (1f)] catalyze the formation of n-propylbenzene and cumene from benzene and propene. The catalysts are selective for branched products, and the cumene/n-propylbenzene ratio decreases with increasing donor ability of the xbpy ligand. DFT(D) calculations predict more favorable activation barriers for 1,2-insertion into the Pt-Ph bond to give branched products. The calculations indicate that 1,2-insertion of propene should be faster than 2,1-insertion for all Pt(II) catalysts studied, but they also indicate that cumene/n-propylbenzene selectivity is under Curtin-Hammett control.
- McKeown, Bradley A.,Prince, Bruce M.,Ramiro, Zoraida,Gunnoe, T. Brent,Cundari, Thomas R.
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p. 1607 - 1615
(2014/05/20)
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- HETEROCYCLIZATION OF β,γ-DICHLORO KETONES AS A METHOD FOR THE SYNTHESIS OF FURAN DERIVATIVES
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Dichloro ketones obtained from acyl chlorides and allyl or β-methylallyl chloride undergo spontaneous cyclization to give 2-alkyl- and 2,4-dialkylfurans when they are heated; the intermediates in the case of 2,3-dichloropropene split out a molecule of hydrogen chloride to give 3,4-dichloro-2-butenones.
- Mamedov, E. J.,Ismailov, A. G.,Kozhushkov, S. I.,Zefirov, N. S.
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p. 260 - 265
(2007/10/02)
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- CHEMISTRY OF SYSTEMS OF THE ALLYLIC TYPE II. ACYLATION OF 3-BROMO- AND 2-METHYL-3-CHLORO-1-PROPENES
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The acylation of 3-bromo- and 2-methyl-3-chloro-1-propenes under the conditions of the Kondakov-Krapivin reaction showed that the addition of acyl chlorides to these compounds takes place according to the Markovnikov rule with formation of the corresponding halogen-containing α-β-unsaturated ketones and alkyl(cycloalkyl)furans.
- Ibragimov, I. I.,Mamedov, E. I.,Ismailov, A. T.,Aliev, A. G.,Mekhtieva, Sh. Z.,et al.
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p. 1425 - 1430
(2007/10/02)
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- Gas-phase Heteroaromatic Substitution. Part 6. Alkylation of Pyrrole, N-Methylpyrrole, Furan, and Thiophene by Isopropyl Cation
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Isopropyl cation, obtained in the dilute gas state from the γ-radiolysis of propane, has been allowed to react with pyrrole (1), N-methylpyrrole (2), furan (3), and thiophene (4), both neat and in competition with benzene, in the pressure range 50-760 Torr, and in the presence of variable concentrations of a gaseous base (NMe3).Both the reactivity of the selected heteroatomic compounds and the isomeric distribution of their isopropylated derivatives depend upon the total pressure of the system and the concentration of NMe3.The apparent heteroaromatic substrate (S) vs. benzene (B) selectivity kS/kB ratios decrease slightly with increasing pressure.At atmospheric pressure, the kS/kB ratios for pyrroles are found to increase with NMe3 concentrations reaching a value of 0.7 (1) and 0.8 (2) at the highest base concentration .The kS/kB values concerning furan and thiophene are found to decrease slightly with the NMe3 concentration, levelling off to 0.3 (3) and 0.8 (4) at P(NMe3) 10 Torr.Under the same conditions, predominant β substitution takes place in pyrroles , whereas α-attack is favoured in the case of furan (β:α 29:71).Thiophene (4) displays no significant positional discrimination (β:α 49:51).The mechanism of substitution, and the subsequent isomerization and dealkylation processes, are discussed, and the substrate and positional selectivity of i-C3H7+ compared with that of related gaseous alkylating reactants.The hypothesis of gas-phase electrophilic alkylation reactions of simple five-membered heteroaromatic compounds regulated essentially by electrostatic interations within the encounter pair is confirmed in the present study.
- Laguzzi, Giuseppe,Speranza, Maurizio
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p. 857 - 866
(2007/10/02)
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