- Bis(3,4-dimethoxybenzyl) ether and tetramethoxy-4,4′-(2,3-dimethyltetramethylene)-dipyrocatechol
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In molecules of both bis(3,4-dimethoxybenzyl) ether, C18H22O5, (I), and meso-tetramethoxy-4,4′-(2,3-dimethyltetramethylene)dipyrocatechol, C22H30O4, (II), the methoxy groups are almost copl
- Fun, Hoong-Kun,Chinnakali, Kandasamy,Sivakumar, Kandasamy,Sam, Teng-Wah,How, Siew-Eng
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- Synthesis of cycloveratrylene macrocycles and benzyl oligomers catalysed by bentonite under microwave/infrared and solvent-free conditions
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Tonsil Actisil FF, which is a commercial bentonitic clay, promotes the formation of cycloveratrylene macrocycles and benzyl oligomers from the corresponding benzyl alcohols in good yields under microwave heating and infrared irradiation in the absence of solvent in both cases. The catalytic reaction is sensitive to the type of substituent on the aromatic ring. Thus, when benzyl alcohol was substituted with a methylenedioxy, two methoxy or three methoxy groups, a cyclooligomerisation process was induced. Unsubstituted, methyl and methoxy benzyl alcohols yielded linear oligomers. In addition, computational chemistry calculations were performed to establish a validated mechanistic pathway to explain the growth of the obtained linear oligomers.
- Miranda, Rene,Valencia-Vazquez, Omar,Maya-Vega, Carlos Abel,Nicolas-Vazquez, Ines,Vargas-Rodriguez, Yolanda Marina,Morales-Serna, Jose Antonio,Garcia-Rios, Erendira,Salmon, Manuel
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p. 12820 - 12844
(2013/11/06)
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- The role of aromatic radical cations and benzylic cations in the 2,4,6-triphenylpyrylium tetrafluoroborate photosensitized oxidation of ring-methoxylated benzyl alcohols in CH2Cl2 solution
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A steady-state and laser flash photolysis (LFP) study of the TPPBF 4-photosensitized oxidation of ring-methoxylated benzyl alcohols has been carried out. Direct evidence on the involvement of intermediate benzyl alcohol radical cations and benzylic cations in these reactions has been provided through LFP experiments. The reactions lead to the formation of products (benzaldehydes, dibenzyl ethers, and diphenylmethanes) whose amounts and distributions are influenced by the number and relative position of the methoxy substituents. This behavior has been rationalized in terms of the interplay between the stabilities of benzyl alcohol radical cations and benzyl cations involved in these processes. A general mechanism for the TPPBF 4-photosensitized reactions of ring-methoxylated benzyl alcohols has been proposed, where the a-OH group of the parent substrate acts as the deprotonating base promoting α-C-H deprotonation of the benzyl alcohol radical cation (formed after electron transfer from the benzyl alcohol to TPP*) to give a benzyl radical and a protonated benzyl alcohol, precursor of the benzylic cation. This hypothesis is in contrast with previous studies, where formation of the benzyl cation was suggested to occur from the neutral benzyl alcohol through the Lewis acid action of excited TPP+ (TPP*).
- Branchi, Barbara,Bietti, Massimo,Ercolani, Gianfranco,Angeles Izquierdo,Miranda, Miguel A.,Stella, Lorenzo
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p. 8874 - 8885
(2007/10/03)
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- Electrostatic catalysis by ionic aggregates: Scope and limitations of Mg(ClO4)2 as acylation catalyst
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Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO4) 2>Ba(ClO4)2>LiClO4. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO4) 2. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.
- Chakraborti, Asit K.,Sharma, Lalima,Gulhane, Rajesh,Shivani
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p. 7661 - 7668
(2007/10/03)
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