- A Baker-Venkataraman retro-Claisen cascade delivers a novel alkyl migration process for the synthesis of amides
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A simple extension of the carbamoyl Baker-Venkataraman rearrangement has been developed. If residual water in the reaction is not strictly excluded a Baker-Venkataraman retro-Claisen cascade takes place, giving amide products, in which an alkyl group apparently migrates between two functionalities of the substrate.
- Ameen, Dana,Snape, Timothy J.
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supporting information
p. 1816 - 1819
(2015/03/30)
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- Rhodium(III)-catalyzed dehydrogenative Heck reaction of salicylaldehydes
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Your CHOice! An efficient RhIII-catalyzed dehydrogenative Heck reaction (DHR) of salicylaldehydes with different classes of olefins extends the oxidative Heck reaction to aldehyde C-H bonds. Several structural motifs similar to natural products and bioactive molecules such as aurones, flavones, 2'-hydroxychalcones, and flavanones could be efficiently produced. Initial mechanistic studies give insight into the reaction mechanism. Copyright
- Shi, Zhuangzhi,Schr?der, Nils,Glorius, Frank
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supporting information; experimental part
p. 8092 - 8096
(2012/08/29)
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- Microwave-induced deactivation-free catalytic activity of BEA zeolite in acylation reactions
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Solventless liquid-phase acylation of p-cresol with different aliphatic carboxylic acids like acetic, propionic, butyric, hexanoic, octanoic, and decanoic acids was investigated over BEA zeolite under conventional as well as microwave heating. An unanticipated huge difference in activity was observed between two modes of heating. Under conventional heating, conversion of all the acids was less than 20%, while under microwave heating, the conversion was in the range of 50-80%. Ester formed through O-acylation and ortho-hydroxyketone formed through Fries rearrangement of the ester were the only products. Conversion of carboxylic acid increased with chain length up to hexanoic acid and then it showed a decrease in the trend. With all the acids, O-acylation occurred rapidly followed by slow conversion to ortho-hydroxyketone. The ketone/ester ratio increased with catalyst amount, temperature, and reaction time. Used catalyst samples were characterized by TGA, XRD, and IR studies to understand lower activity and deactivation behavior under conventional heating. The results showed absence of coke precursor/coke on the catalyst used in microwave-irradiated reactions in contrast to catalyst used in conventionally heated ones. Higher yield in the case of microwave-assisted reactions is attributed to the prevention of coke precursor/coke on the active sites by microwaves.
- Chandra Shekara,Jai Prakash,Bhat
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scheme or table
p. 101 - 107
(2012/07/14)
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- Intramolecular ketone-olefin radical cyclization with low-valent titanium reagent: Synthesis of benzopyrans
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A novel protocol for intramolecular ketyl-olefin radical cyclization with low-valent titanium reagent is outlined. It allows the formation of the benzopyran nucleus from ortho-allyloxy propiophenones as the sole product in moderate yields via intramolecular radical cyclization. Copyright Taylor & Francis Group, LLC.
- Nayak, Sandip K.,Bhatt, Suchitra,Roy, Kshama
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scheme or table
p. 2969 - 2975
(2010/11/05)
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- A comparative study: One pot synthesis of some prochiral ketones using conventional and microwave assisted methods
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Polyphosphoric acid (PPA) has been used to synthesize a number of prochiral aryl ketones as well as α,β-unsaturated diaryl ketones by conventional and microwave assisted methods in moderate to good yield. The microwave assisted method is advantageous due to increased yield and high purity of products within incredible short period of time.
- Salokhe,Mote,Suryavanshi,Salunkhe
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experimental part
p. 1347 - 1351
(2010/07/05)
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- Regioselective ortho-acylation of phenol and naphthol derivatives catalyzed by FeCl3 under microwave conditions
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Phenol and naphthol derivatives were subjected to regioselective solvent-free ortho-acylation with organic acids in the presence of FeCl 3 under microwave irradiation. The reactions were complete in a short time, and the products were obtained in high yields.
- Naeimi,Moradi
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body text
p. 1757 - 1759
(2009/09/29)
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- Microwave assisted direct ortho-acylation of phenol and naphthol derivatives by BF3·(C2H5)2O
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The solventless acylation of phenol and naphthol derivatives with various organic acids and BF3·(C2H5) 2O, under microwave conditions, was studied. High yields of the o-acylated products were achieved in a very short time.
- Naeimi, Hossein,Moradi, Leila
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p. 284 - 287
(2008/02/04)
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- Rate of Enolate Formation Is Not Very Sensitive to the Hydrogen Bonding Ability of Donors to Carboxyl Oxygen Lone Pair Acceptors; A Ramification of the Principle of Non-Perfect Synchronization for General-Base-Catalyzed Enolate Formation
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Two series of structures (1 and 2) possessing intramolecular hydrogen bonds to the lone-pair electrons of carbonyl oxygens have been examined to reveal the influence of the pKa of the hydrogen-bond donor on the rate of general-base-catalyzed enolate formation. The geometry of the hydrogen bonds is well accepted to be appropriate for intramolecular hydrogen-bond formation. Yet, as revealed by Bronsted plots, both series show very little dependence of the rate of enolate formation on the hydrogen-bond donor ability. The intramolecular hydrogen bonds give rate enhancements only on the order of 10-100-fold, and corrected Bronsted α-values are slightly below 0.1. The results can be understood by interpreting them in light of the Principle of Non-Perfect Synchronization. The results are consistent with the proton transfer occurring through an asynchronous transition state with the developing negative charge localized on carbon. We postulate that catalysts of enolate formation will be most effective if the binding groups are focused on stabilizing negative charge that is forming on the enolate carbon rather than on the enolate oxygen.
- Zhong, Zhenlin,Snowden, Timothy S.,Best, Michael D.,Anslyn, Eric V.
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p. 3488 - 3495
(2007/10/03)
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- A REEXAMINATION OF THE RETRO-FRIES REARRANGEMENT OF SOME o-HYDROXYKETONES
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The retro-Fries rearrangement, catalyzed by protic and Lewis acids, was studied for some o-hydroxyketones.The results are consistent with the mechanism of an heterolytic cleavage and rearrangement.It appears that, in general, Lewis acids do not induce the retro-Fries rearrangement of o-hydroxyketones.However, in certain cases, it may be brought about the presence of a protic acid generated in situ, from a solvent-catalyst interaction.
- Martin, Robert,Lafrance, Jean Ronald,Demerseman, Pierre
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p. 539 - 548
(2007/10/02)
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- Lewis Acids Catalysed Fries Rearrangement of Isopropylcresol Esters
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In the course of the Fries rearrangement, aluminium chloride frequently induces migration or elimination of alkyl groups.The results obtained with titanium tetrachloride for the synthesis of vicinal o-hydroxyketones are compared with those obtained with aluminium chloride for some aliphatic and aromatic esters of isopropylcresols.In order to understand the migration and elimination processes occurring, the stabilities of the o-hydroxyketones are studied in the presence of aluminium chloride at different temperatures.Furthermore, all-vicinal o-hydroxyketones were prepared by the Fries rearrangement of 6-tert-butyl-p-thymol with titanium tetrachloride.
- Martin, Robert,Demerseman, Pierre
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p. 227 - 236
(2007/10/02)
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- Synthesis, Spectral Data and Extraction of Copper by 1-(2'-Hydroxy-5'-alkylphenyl)-1-alkanone Oximes
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1-(2'-Hydroxy-5'-alkylphenyl)-1-ethanone oximes with a normal alkyl group containing 2 to 12 carbon atoms and 1-(2'-hydroxy-5'-methylphenyl)-1-alkanone oximes containing 1 to 11 carbon atoms in the hydrocarbon chain were synthesized.Spectral data (u.v., i.r., n.m.r. and 13C) of oximes are reported.Four of these oximes were used for copper extraction from acidic solution.The results obtained indicate, that these oximes are better extractants than alkyl derivatives of 2-hydroxybenzophenone oximes.
- Krzyzanowska, Ewa,Olszanowski, A.,Juskowiak, M.
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p. 617 - 630
(2007/10/02)
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- THE SYNTHESIS OF 4H-PYRAN CONTAINING HEMISPHERANDS VIA PYRYLIUM SALTS
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Two new hemispherands 2a and 2b containing a central 4H-pyran unit were synthesized via appropiately substituted 2,6-phenyl pyrylium salts; largest ΔG0 values of complexation of 2a and 2b with different alkali picrates are found for Na(+) and K(+).
- Dijkstra, P. J.,Steen, B. J. van,Hams, B. H. M.,Hertog, H. J. den,Reinhoudt, D. N.
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p. 3183 - 3186
(2007/10/02)
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