- The influence of the acidity of ionic liquids on catalysis
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Reactions performed in ionic liquids with BF4- as anion progress under strongly acidic conditions. The acidity of some air- and moisture-stable ionic liquids is explored and its effect on catalytic reactions is studied. The function of these ionic liquids in some traditional acid-catalyzed reactions is also tested, and the results merit a reconsideration of their influence on catalytic reactions and use in other applications.
- Cui, Xinjiang,Zhang, Shiguo,Shi, Feng,Zhang, Qinghua,Ma, Xiangyuan,Lu, Liujin,Deng, Youquan
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Read Online
- Electrophilic Substitution in Pyrroles. Part 4. Hydrogen Exchange in Acid Solution
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Hydrogen exchange at the unsubstituted positions in 1,2,5-trimethyl- and 1,3,4-trimethyl-pyrrole in aqueous buffer has been examined.The two positions were found to be of similar reactivities.General acid catalysis was detected.No hydrogen exchange on the methyl groups of 2,3,4,5-tetramethylpyrrole, even in strong acid, was detected.The 13C n.m.r. spectrum of the tetramethylpyrrole was examined.
- Alexander, Robert s.,Butler, Anthony R.
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Read Online
- Zeolites Catalyze the Nazarov Reaction and the tert -Butylation of Alcohols by Stabilization of Carboxonium Intermediates
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Zeolites are the most used catalysts worldwide in petrochemistry processes, with particular ability to stabilize carbocations. However, the use of zeolites in organic synthesis is still scarce. We show here that representative carboxonium-mediated organic
- Blake, Finn,Leyva-Pérez, Antonio,Sanz-Navarro, Sergio,Tejeda-Serrano, María
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p. 2031 - 2037
(2020/07/14)
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- Hydrosilylation of carbonyl and carboxyl groups catalysed by Mn(i) complexes bearing triazole ligands
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Manganese(i) complexes bearing triazole ligands are reported as catalysts for the hydrosilylation of carbonyl and carboxyl compounds. The desired reaction proceeds readily at 80 °C within 3 hours at catalyst loadings as low as 0.25 to 1 mol%. Hence, good to excellent yields of alcohols could be obtained for a wide range of substrates including ketones, esters, and carboxylic acids illustrating the versatility of the metal/ligand combination.
- Martínez-Ferraté, Oriol,Chatterjee, Basujit,Werlé, Christophe,Leitner, Walter
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p. 6370 - 6378
(2019/11/20)
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- The Guanidine-Promoted Direct Synthesis of Open-Chained Carbonates
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In order to reduce CO2 accumulation in the atmosphere, chemical fixation methodologies were developed and proved to be promising. In general, CO2 was turned into cyclic carbonates by cycloaddition with epoxides. However, the cyclic carbonates need to be converted into open-chained carbonates by transesterification for industrial usage, which results in wasted energy and materials. Herein, we report a process catalyzed by tetramethylguanidine (TMG) to afford linear carbonates directly. This process is greener and shows potential for industrial applications.
- Shang, Yuhan,Zheng, Mai,Zhang, Haibo,Zhou, Xiaohai
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p. 933 - 938
(2019/09/30)
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- Synthesis of Benzyl Alkyl Ethers by Intermolecular Dehydration of Benzyl Alcohol with Aliphatic Alcohols under the Effect of Copper Containing Catalysts
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Synthesis of benzyl alkyl ethers was performed in high yields by intermolecular dehydration of benzyl and primary, secondary, tertiary alcohols under the effect of copper containing catalysts. The formation of benzyl alkyl ethers occurs with participation of benzyl cation.
- Bayguzina,Gimaletdinova,Khusnutdinov
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p. 1148 - 1155
(2018/10/24)
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- Palladium on Carbon-Catalyzed Benzylic Methoxylation for Synthesis of Mixed Acetals and Orthoesters
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The palladium on carbon (Pd/C)-catalyzed direct methoxylation of the benzylic positions of linear benzyl and cyclic ether substrates proceeded in the presence of i-Pr2NEt under an oxygen atmosphere to give the corresponding mixed acetals. Cyclic acetal derivatives could also be converted into orthoesters. The present direct methoxylation via a carbon-hydrogen (C?H) functionalization can be accomplished using the easily-removed Pd/C and molecular oxygen as a green oxidant. The obtained mixed acetals were transformed into the corresponding ether products by chemoselective substitution of the methoxy group using a silyltriflate, 2,4,6-collidine, and a nucleophile. The orthoester derivative could also be transformed into the cyclic ketal under similar reaction conditions.
- Yasukawa, Naoki,Kanie, Takafumi,Kuwata, Marina,Monguchi, Yasunari,Sajiki, Hironao,Sawama, Yoshinari
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supporting information
p. 10974 - 10977
(2017/08/22)
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- Auto-Tandem Catalysis with Frustrated Lewis Pairs for Reductive Etherification of Aldehydes and Ketones
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Herein we report that a single frustrated Lewis pair (FLP) catalyst can promote the reductive etherification of aldehydes and ketones. The reaction does not require an exogenous acid catalyst, but the combined action of FLP on H2, R-OH or H2O generates the required Br?nsted acid in a reversible, “turn on” manner. The method is not only a complementary metal-free reductive etherification, but also a niche procedure for ethers that would be either synthetically inconvenient or even intractable to access by alternative synthetic protocols.
- Bakos, Mária,Gy?m?re, ádám,Domján, Attila,Soós, Tibor
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supporting information
p. 5217 - 5221
(2017/04/27)
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- METHOD FOR PRODUCING ASYMMETRIC ALKYL ETHER HAVING TERTIARY ALKYL GROUP
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PROBLEM TO BE SOLVED: To provide a method capable of obtaining an asymmetric alkyl ether having a tertiary alkyl group easily and industrially. SOLUTION: (1) There is provided a method for producing an asymmetric alkyl ether having a tertiary alkyl group by subjecting a tertiary alcohol and a primary alcohol or a secondary alcohol to a dehydration reaction using activated clay as a catalyst. (2) There is provided the method for producing an asymmetric alkyl ether having a tertiary alkyl group according to (1), where the tertiary alcohol is any one selected from the group consisting of tert-butanol, tert-amylalcohol and 1-adamantyl alcohol. SELECTED DRAWING: None COPYRIGHT: (C)2016,JPOandINPIT
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Paragraph 0029
(2017/01/31)
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- Gold(I)-catalyzed synthesis of unsymmetrical ethers using alcohols as alkylating reagents
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A microwave-irradiated alcohol-protecting strategy based on gold catalysis utilizing benzyl alcohol, tert-butyl alcohol and triphenylmethanol as alkylating reagents has been developed. This protecting strategy has wide functional group tolerance with satisfactory yields for the majority of the selected alcohols. The mechanism of this transformation was probed with oxygen-18 isotope labelled alcohols assisted by GC-MS techniques and chemical kinetic experiments. This strategy provides an efficient, straightforward and alternative approach to the preparation of benzyl, tert-butyl and trityl ethers in organic synthesis.
- Liu, Yongxiang,Wang, Xiaoyu,Wang, Yanshi,Du, Chuan,Shi, Hui,Jin, Shengfei,Jiang, Chongguo,Xiao, Jianyong,Cheng, Maosheng
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p. 1029 - 1036
(2015/03/30)
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- Organohalide-catalyzed dehydrative O-alkylation between alcohols: A facile etherification method for aliphatic ether synthesis
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Organohalides are found to be effective catalysts for dehydrative O-alkylation reactions between alcohols, providing selective, practical, green, and easily scalable homo- and cross-etherification methods for the preparation of useful symmetrical and unsymmetrical aliphatic ethers from the readily available alcohols. Mechanistic studies revealed that organohalides are regenerated as reactive intermediates and recycled to catalyze the reactions.
- Xu, Qing,Xie, Huamei,Chen, Pingliang,Yu, Lei,Chen, Jianhui,Hu, Xingen
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supporting information
p. 2774 - 2779
(2015/05/27)
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- Acid- and isobutylene-free synthesis of t-butyl ethers by in situ formation of 2-t-butoxy-1-methylpyridinium triflate
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The title reagent is formed in situ by alkylation of 2-t-butoxypyrine. The subsequent addition of an alcohol substrate leads to the formation of t-butyl ethers without the need for isobutylene gas or acid activators.
- Salvati, Anna E.,Hubley, Christian T.,Albiniak, Philip A.
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supporting information
p. 7133 - 7135
(2015/01/08)
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- An efficient synthesis of tert-butyl ethers/esters of alcohols/amino acids using methyl tert-butyl ether
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A facile synthesis of a wide variety of tert-butyl ethers and tert-butyl ester derivatives under mild conditions is described. Alcohols etherified with tert-butyl methyl ether as tert-butyl source and solvent, in the presence of sulfuric acid. Many amino acid tert-butyl esters have been synthesized by this procedure. The reaction is simple, inexpensive, easily scaled up, and proceeds without observable racemization. A green method was developed for the deprotection of this group using Amberlite resin IR 120-H as catalyst.
- Mallesha,Prahlada Rao,Suhas,Channe Gowda
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experimental part
p. 641 - 645
(2012/02/15)
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- Triflic acid catalyzed reductive coupling reactions of carbonyl compounds with O-, S-, and N-nucleophiles
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Highly efficient metal-free reductive coupling reactions of aldehydes and ketones with a range of nucleophiles in the presence of triflic acid (1-5 mol %) as the catalyst are presented. The reactions can be performed at ambient temperature without exclusion of moisture or air. A range of symmetrical and unsymmetrical ethers were obtained by this method in high yields and short reaction times. For the first time, the influence of additional functionalization has been studied. Furthermore, the formation of thioethers from ketones (by addition of unmodified thiols) and of sulfonamides from either aldehydes or ketones has been achieved under catalytic conditions.
- Gellert, Beate A.,Kahlcke, Nils,Feurer, Markus,Roth, Stefanie
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supporting information; experimental part
p. 12203 - 12209
(2011/11/07)
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- Carbon halide bond activation of benzyl chloride and benzyl bromide using An NHC-stabilized nickel(0) complex
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A first example of the application of an NHC-stabilized nickel complex as a catalyst in Suzuki-Miyaura cross-coupling reactions of alkyl halides is reported. The complexes trans-[Ni(iPr2Im)2(X)(CH 2Ph)] (X = Cl 2 and Br 3) were prepared from the reactions of benzyl chloride and benzyl bromide and the dinuclear complex [Ni2(iPr 2Im)4(COD)] (1). These compounds were fully characterized by elemental analysis, IR spectroscopy, multinuclear NMR spectroscopy, and X-ray crystallography. Based on these stoichiometric oxidative addition reactions catalytic Suzuki-Miyaura cross-coupling reactions have been performed. Complex 1 is an effective catalyst for the Suzuki-Miyaura cross-coupling reaction of benzyl chloride and phenylboronic acid. Quantitative conversion of benzyl chloride with a high selectivity to the cross-coupling product diphenylmethane was achieved after two hours reaction time using three equivalents phenylboronic acid, three equivalents cesium fluoride and 1.22 mol-% [Ni2(iPr 2Im)4(COD)] (1) as a catalyst. Copyright
- Zell, Thomas,Radius, Udo
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scheme or table
p. 1858 - 1862
(2012/01/12)
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- Ferric perchlorate as an efficient and useful catalyst for the selective benzylation and methylation of alcohols with benzyl chloride and methyl iodide
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A mild and efficient method was developed for selective benzylation and methylation of hydroxyl compounds in the presence of a catalytic amount of ferric perchlorate. We showed that ferric perchlorate was very effective in selectively promoting the benzylation and methylation of primary aliphatic and benzylic alcohols versus secondary aliphatic alcohols and phenolic hydroxy groups. Graphical abstract: [Figure not available: see fulltext.]
- Behbahani, Farahnaz K.,Heravi, Majid M.,Oskooie, Hossien A.
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experimental part
p. 181 - 184
(2010/03/26)
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- Gold-catalyzed substitution reaction with ortho-alkynylbenzoic acid alkyl ester as an efficient alkylating agent
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ortho-Alkynylbenzoic acid alkyl esters behave as alkylating agents in combination with gold catalysts. The reaction with alcohols occurs smoothly in the presence of catalytic amounts of Ph3PAuCl and AgOTf under mild conditions to produce the corresponding ether products in high yields. The protocol is also useful for Friedel-Crafts alkylation and N-alkylation of sulfonamides. The reaction likely proceeds through the gold-induced in situ construction of leaving groups and subsequent nucleophilic attack of nucleophiles, such as alcohols, aromatic compounds, and sulfonamides.
- Aikawa, Haruo,Tago, Sakie,Umetsu, Kazuteru,Haginiwa, Naomichi,Asao, Naoki
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experimental part
p. 1774 - 1784
(2009/06/20)
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- A convenient synthesis of tert-butyl ethers under microwave condition
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Synthesis of tert-butyl ethers from various alcohols and substituted phenols can be achieved using tert-butyl bromide in the presence of basic lead carbonate as a catalyst under microwave irradiation in absence of solvent. The catalyst is easily recovered via filtration and reused up to three times without appreciable loss of activity.
- Mahammed,Keshava Murthy,Mohana Raju
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p. 575 - 578
(2008/09/20)
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- Efficient synthesis of tert-butyl ethers under solvent-free conditions
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A simple and efficient synthesis of tert-butyl ethers from various alcohols and substituted phenols using tert-butyl bromide in the presence of basic lead carbonate as a catalyst. The catalyst is easily recovered via filtration and can be reused up to three times without appreciable loss of activity. Copyright Taylor & Francis Group, LLC.
- Rai, Neithnadka Premsai,Arunachalam, Pirama Nayagam
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p. 2891 - 2896
(2008/02/13)
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- A direct functionalization of tertiary alkyl bromides with O-, N-, and C-nucleophiles
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Silver oxide used in stoichiometric amounts promoted the direct functionalization of tert-alkyl bromides and provided the desired adducts in 39-96% isolated yield. Reaction of tert-bromides with carboxylic acids yielded esters, with alcohols and phenols yielded alkyl and aryl ethers, with amines and anilines yielded selectively mono-alkylated amines and anilines, and with a C-nucleophile yielded an all-carbon quaternary hydrocarbon. The method was applied to a sequential alkylation of a primary amine with two different alkyl bromides yielding selectively a tertiary amine with three different substituents in one-pot.
- Vachal, Petr,Fletcher, Joan M.,Hagmann, William K.
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p. 5761 - 5765
(2008/02/09)
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- Gold-catalyzed etherification and friedel - Crafts alkylation using ortho-alkynylbenzoic acid alkyl ester as an efficient alkylating agent
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A gold-catalyzed alkylation of alcohols and aromatic compounds is described. The reaction of ortho-alkynylbenzoic acid alkyl esters with alcohols or aromatic compounds occurs in the presence of catalytic amounts of Ph 3PAuCl and AgOTf under mild conditions to produce corresponding ethers or Friedel-Crafts alkylation products in good to high yields. The reaction likely proceeds through the gold-induced in situ construction of leaving groups and subsequent nucleophilic attack of alcohols or aromatic compounds.
- Asao, Naoki,Aikawa, Haruo,Tago, Sakie,Umetsu, Kazuteru
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p. 4299 - 4302
(2008/02/12)
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- Intermolecular reactions of chlorohydrine anions: Acetalization of carbonyl compounds under basic conditions
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Nonenolizable aldehydes and ketones react with 2-chloroethanol and 3-chloropropanol under basic conditions (t-BuOK, DMF/THF) with formation of 2-substituted 1,3-dioxolanes and 1,3-dioxanes, respectively. Conversion of the two-step addition-alkylation process depends on the electrophilicity of the carbonyl group that governs the equilibrium of addition of chloroalkoxides. This method of protection of carbonyl groups in the form of cyclic acetals under kinetically controlled conditions is complementary to the acid-catalyzed reaction with diols.
- Barbasiewicz, Michal,Makosza, Mieczyslaw
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p. 3745 - 3748
(2007/10/03)
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- Unusual and unexpected reactivity of t-butyl dicarbonate (Boc2O) with alcohols in the presence of magnesium perchlorate. A new and general route to t-butyl ethers
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(Chemical Equation Presented) A new mild method for protecting alcohols as t-butyl ethers is reported. The reaction proceeds with Mg(ClO4) 2 and Boc2O and shows general applicability. The deprotection of t-butyl ethers has also been revisited. Preliminary results indicate the CeCl3·7H2O/Nal system is a very suitable catalyst for their removal.
- Bartoli, Giuseppe,Bosco, Marcella,Locatelli, Manuela,Marcantoni, Enrico,Melchiorre, Paolo,Sambri, Letizia
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p. 427 - 430
(2007/10/03)
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- Thermochemistry of benzyl alcohol: Reaction equilibria involving benzyl alcohol and tert-alkyl ethers
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Chemical equilibrium of the reactive systems of benzyl alcohol with tert-alkyl ethers was studied in the liquid phase in the temperature range (298 to 373) K and with a cation exchanger Amberlist 15 as a catalyst. Enthalpies of reactions involving benzyl alcohol were obtained from the temperature dependence of the equilibrium constants according to the Second Law and used to derive averaged standard enthalpies of formation of benzyl alcohol ΔfHm(1,298.15K) = -(154-5 ± 1.7) kJ·mol-1 in the liquid state. Vapor pressures and enthalpy of vaporization, ΔlgH m(298.15 K), of benzyl alcohol were determined using transpiration method. The latter value, together with the reliable literature data, provided an averaged result ΔlgHm(298.15 K) = (65.75 ± 0.51) kJ·mol-1. Both averaged results for ΔfHm(1,298.15K)o and ΔfHm(298.15 K) were used to calculate and to recommend the value of enthalpy of formation of benzyl alcohol in the gaseous state ΔfHm(298.15K)o = -(88.8 ± 1.8) kJ·mol-1. Auxiliary data for tert-butyl benzyl ether (energy of combustion, vapor pressures, and enthalpy of vaporization) were measured using calorimetry and transpiration method.
- Verevkin, Sergey P.,Vasiltsova, Tatiana V.
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p. 1717 - 1723
(2007/10/03)
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- Oxidation of benzylic alcohols and ethers to carbonyl derivatives by nitric acid in dichloromethane
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Nitric acid in dichloromethane may be successfully employed for the oxidation of benzylic alcohols and ethers to the corresponding carbonyl compounds. The proposed method proved to be of general applicability, affording very good yields of aldehydes and ketones and showing interesting chemoselectivity in many instances, allowing competitive aromatic nitration to be avoided, as well as - in the case of aldehydes - any further oxidation to carboxylic acids. The reaction probably proceeds by a radical mechanism, the active species in the oxidation process being NO2. Competitive formation of nitro esters was observed in some cases, whereas poor results were obtained with allylic and non-benzylic substrates. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Strazzolini, Paolo,Runcio, Antonio
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p. 526 - 536
(2007/10/03)
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- BiBr3, an efficient catalyst for the benzylation of alcohols: 2-Phenyl- 2-propyl, a new benzyl-type protecting group
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The benzylation of aliphatic alcohols with various benzylic alcohols has been achieved in the presence of BiBr3 under mild conditions. 2- Phenylpropan-2-ol proved to be the most efficient and can be considered as a novel protecting group. (C) 2000 Elsevier Science Ltd.
- Boyer, Bernard,Keramane, El-Mehdi,Roque, Jean-Pierre,Pavia, André A.
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p. 2891 - 2894
(2007/10/03)
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- Secondary α-Deuterium Kinetic Isotope Effects Signifying a Polar Transition State in the Thermolysis of Ring-Substituted tert-Butyl Phenylperacetates
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Several ring-substituted tert-butyl phenylperacetates (YC6H4CH2CO3But) and their deuterated versions (YC6H4CD2CO3But) were prepared (Y: p-OCH3, p-CH3, p-H, and p-NO2). Thermolyses at 80°C in CDCl3 showed excellent first-order kinetics. The rates have been measured as kYH × 104 and kYD × 104 s-1: 11.9 and 9.20 (p-OCH3), 2.64 and 2.22 (p-CH3), 1.06 and 0.93 (p-H), 0.164 and 0.156 (p-NO2). Hammett correlations were derived to yield ρYH+ = -1.17 and ρYD+ = -1.12. However, better Hammett plots were obtained with three points (p-OCH3, p-CH3, and p-H) showing ρYH+ = -1.35 and ρYD+ = -1.28. SDKIE was calculated as 1.293 (p-OCH3), 1.189 (p-CH3), 1.140 (p-H), and 1.051 (p-NO2), showing substantial substituent effects. Values of kYH/kYD for p-NO2 showed little temperature dependence. Hammett correlations and SDKIE were derived from the same kinetic entity that is the bond cleavage.
- Kim, Sung Soo,Tuchkin, Alexey
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p. 3821 - 3824
(2007/10/03)
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- Thermolysis of substituted tert-butyl-(2-phenyl-prop-2-yl) peroxides
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tert-Butyl-(2-phenyl-1-methoxy-prop-2-yl)-peroxide (1a), tert-butyl-(2-phenyl-1-acetoxy-prop-2-yl)-peroxide (1b) and tert-butyl-(1,2-diphenyl-prop-2-yl)-peroxide (1c) were prepared from t-BuOOH and 1-methoxy-2-phenyl-prop-2-ol (a), 2-phenyl-2-methyl-oxirane (b) and, respectively, 1,2-diphenyl-propan-2-ol (c). The peroxides 1a-c were characterized by NMR spectroscopy and elemental analysis. Kinetic data were determined and the products analyzed from thermolysis of 1a-c at 110-155°C in cumene as the solvent. The major thermolysis product from 1a-c was acetophenone, formed via fragmentation of intermediate alkoxy radicals: R-CH2-C(Ph)(Me)O (R: MeO (a); AcO (b); Ph (c)). Wiley-VCH Verlag GmbH, 1999.
- Suprun
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p. 363 - 368
(2007/10/03)
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- Convenient preparations of t-butyl esters and ethers from t-butanol
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A one-pot preparation of t-butyl esters and ethers is described that proceeds from the carboxylic acid or alcohol and t-butanol using only anhydrous magnesium sulfate and catalytic sulfuric acid as additional reagents. The method affords t-butyl esters and ethers in good yields and is applicable to a variety of substrates.
- Wright, Stephen W.,Hageman, David L.,Wright, Ann S.,McClure, Lester D.
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p. 7345 - 7348
(2007/10/03)
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- Hypervalent (tert-butylperoxy)iodanes generate iodine-centered radicals at room temperature in solution: Oxidation and deprotection of benzyl and allyl ethers, and evidence for generation of α-oxy carbon radicals
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1-(tert-Butylperoxy)-1,2-benziodoxol-3(1H)-one (1a) oxidizes benzyl and allyl ethers to the esters at room temperature in benzene or cyclohexane in the presence of alkali metal carbonates. Since this reaction is compatible with other protecting groups such as MOM, THP, and TBDMS ethers, and acetoxy groups, and because esters are readily hydrolyzed under basic conditions, this new method provides a convenient and effective alternative to the usual reductive deprotection. Oxidation with 1a occurs readily with C-H bonds activated by both enthalpic effects (benzylic, allylic, and propargylic C-H bonds) and/or polar effects (α-oxy C-H bonds), generating α-oxy carbon-centered radicals, which can be detected by nitroxyl radical trapping. Measurement of the relative rates of oxidation for a series of ring-substituted benzyl n-butyl ethers 2d and 2p-s indicated that electron-releasing groups such as p-MeO and p-Me groups increase the rate of oxidation, and Hammett correlation of the relative rate factors with the σ+ constants of substituents afforded the reaction constant ρ+ = -0.30. The large value of the isotope effect obtained for the oxidation of benzyl n-butyl ether 2d (k(H)/k(D) = 12-14) indicates that the rate-determining step of the reactions probably involves a high degree of benzylic C-H bond breaking. The effects of molecular dioxygen were examined, and the mechanism involving the intermediacy of the tert-butylperoxy acetal 5 and/or the hydroperoxy acetal 32 is proposed. Particularly noteworthy is the finding that (tert-butylperoxy)iodane 1a can generate the tert-butylperoxy radical and the iodine-centered radical 33a, even at room temperature in solution, via homolytic bond cleavage of the hypervalent iodine(III)-peroxy bond.
- Ochiai, Masahito,Ito, Takao,Takahashi, Hideo,Nakanishi, Akinobu,Toyonari, Mika,Sueda, Takuya,Goto, Satoru,Shiro, Motoo
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p. 7716 - 7730
(2007/10/03)
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- Efficient reductive etherification of carbonyl compounds with alkoxytrimethylsilanes
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An efficient TMSOTf catalyzed ether synthesis from carbonyl compounds and alkoxytrimethylsilanes via triethylsilane-reduction is described.
- Hatakeyama, Susumi,Mori, Hisato,Kitano, Kaori,Yamada, Hidetoshi,Nishizawa, Mugio
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p. 4367 - 4370
(2007/10/02)
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- A Discriminating Protecting Group Strategy for Alcohols and Amines
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The protection of alcohols and amines as O- and N-benzyl derivatives has long played a central role in organic synthesis.For case where the conventional method of benzylation under strongly base conditions is not applicable, we now describe an alternate method using phenyldiazomethane that proceeds under near-neutral conditions with HBF4 as a catalyst.O-Benzylation occurs at -40 deg C and works well on primary, secondary, and tertiary alcohols.The techique is compatible with ester, acetal, and relative halide functiolatities.Under the same conditions PhCHN2 also N-benzylates primary and secondary amines, albait more slowly.However S-benzylation is only marginally successful.As a consequence aminoalcohols like 2-hydroxymethylpiperidine can be O-benzylayed cleanly and in good yield.Thus HBF4-mediated benzylations using PhCHN2 achieve a kinetic selectivity not customarily possible in the standard Williamson ether synthesis.Preliminary experiments with other, substituted phenyldiazomethanes indicate the method can be extended to the production of substituted benzyl ethers and amines.
- Liotta, Louis J.,Ganem, Bruce
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p. 215 - 222
(2007/10/02)
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- Photochemistry of phosphate esters: An efficient method for the generation of electrophiles
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The photochemical cleavage of benzyl diethyl phosphates, 1a-g, has been examined in tert-butyl alcohol, which produces the corresponding benzyl tert-butyl ether as the major solvolysis product upon direct irradiation. The multiplicity of the reactive excited state has been established as the singlet state. Evidence favoring an intermediate benzyl cation-phosphate ion pair formed from photofragmentation includes oxygen-18 scrambling, racemization of chiral benzyl phosphates, and substituent effects on the rate of reaction. The existence of an electrophilic intermediate is further supported by a linear free energy relationship for the rate of disappearance of 1, kdis, with Hammett σ, which gave a ρ value of -0.90 and for the rate of appearance of 2, kapp, a Hammett ρ value of -0.97. Possible mechanisms including an electron transfer either before or after homolysis or simple heterolysis of the ester bond are evaluated.
- Givens, Richard S.,Matuszewski, Bogdan,Athey, Phillip S.,Robert Stoner
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p. 6016 - 6021
(2007/10/02)
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- SELECTIVE BENZYLATION OF ALCOHOLS AND AMINES UNDER MILD CONDITIONS
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A new synthesis of benzyl ethers and N-benzylamines is described under nonbasic conditions using the fluoboric catalyzed reaction of phenyldiazomethane
- Liotta, Louis J.,Ganem, Bruce
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p. 4759 - 4762
(2007/10/02)
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- Generation of Organic Cations from Group 14 Organometallic Compounds via Photoinduced Electron Transfer in the Presence of Cu(II) Salt
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Irradiations of acetonitrile-alcohol (3:1) solutions of arylmethyl silanes, germane, or stannanes in the presence of Cu(BF4)2 gave alkyl arylmethyl ethers in good yields via arylmethyl cations, The efficiency of this photoreaction increased in the order of Si- Ge- Sn-compounds.
- Mizuno, Kazuhiko,Yasueda, Masahiro,Otsuji, Yoshio
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p. 229 - 232
(2007/10/02)
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- A NEW METHOD FOR THE PREPARATION OF TERTIARY BUTYL ETHERS AND ESTERS
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T-butyl 2,2,2-trichloroacetimidate (1), readily prepared by addition of t-butanol to trichloroacetonitrile, is an efficient reagent for the preparation of t-butyl ethers and esters in the presence of a catalytic amount of boron trifluoride etherate.
- Armstrong, Alan,Brackenridge, Ian,Jackson, Richard F.W.,Kirk, Joanna M.
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p. 2483 - 2486
(2007/10/02)
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- Gas-Phase Wittig Rearrangement of Carbanions Derived from Benzyl Ethers
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The CA mass spectra of ions PhC-HOR and Ph(R)CH-O- (R = alkyl and phenyl) are very similar, suggesting that the Wittig rearrangement PhC-HOEt -> Ph(Et)CH-O- occurs in the gas phase.Major fragmentation can be interpreted in terms of 1,2-elimination of groups from the Wittig product ion.For example, 2H labeling of PhC-HOEt and Ph(Et)CH-O- show that the major processes produce Me-CH=CH-O- + C6H6 and (C6H4)-CHO + C2H6, with the latter process involving prior scrambling of phenyl hydrogens.An analogous process, Ph2CH-O- -> (C6H4)-CHO + C6H6 gives the major peak in the spectrum of "PhC-HOPh".
- Eichinger, Peter C. H.,Bowie, John H.,Blumenthal Thomas
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p. 5078 - 5082
(2007/10/02)
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- Extent of Charge Transfer in the Photoreduction of Phenyl Ketones by Alkylbenzenes
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Rate constants for triplet-state reaction of various ring-substituted benzophenones (BPs), acetophenones (APs), and α,α,α-trifluoroacetophenones (TFAs) with toluene and p-xylene have been determined by a combination of flash kinetics, steady-state quenching, and quantum yield measurements.The relative amounts of primary and tertiary radicals formed by reaction of the same ketons with p-cymene have also been measured.For all three types of ketones, rate constants correlate well with triplet ketone reduction potentials.The magnitude of the kinetic isotope effects observed with toluene-d8 and p-xylene-d10 diminishes as the ketones become easier to reduce.All of the ketone triplets react with alkylbenzenes primarily by a charge-transfer mechanism, with the rate-determining step changing from complexation to hydrogen transfer as the ketones become harder to reduce.The least reactive AP triplets probably react significantly via simple hydrogen atom abstraction as well.Those ketones with n,?* lowest triplets (all BPs and some APs) react with p-cymene to give primary/tertiary radical ratios that vary no more than a factor of 2 from the 0.40 value displayed by tert-butoxy radicals; those with ?,?* lowest triplets (TFAs and some APs) give ratios that favor primary radicals and that vary by an order of magnitude with the triplet ketone reduction potential.The variation in cymene product ratios reflect different orientations for attack on cymene by n,?* and ?,?* triplets and differing degrees of partial electron transfer within the exciplexes, which are not tight radical ion pairs.The variation seen for ?,?* triplets represents a stereoelectronic effect within face-to-face exciples, as evidenced by the excerptional behavior of p-diacylbenzenes, which give the highest ratio of tertiary radicals from cymene.There is no set intrinsic ratio of reactivity for ?,?* triplets vs. n,?* triplets in these CT reactions.The two types of triplets show similar reactivity for the more easily reduced triplets, with the harder to reduce ?,?* triplets being only one-tenth as reactive as n,?* triplets of comparable triplet reduction potential.When the extent of electron transfer in the exciplex is small, hydogen transfer is rate determining and ?,?* reactivity drops.A study of two radical reactions which generate benzyl and α-hydroxy-α-methylbenzyl radicals indicates that radical disproportionation cannot explain the low quantum yields (0.10) of most ketone-toluene photoreductions, which apparently involve substantial radiation less decay by the exciplex intermediates.
- Wagner, Peter J.,Truman, Royal J.,Puchalski, Alan E.,Wake, Ronald
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p. 7727 - 7738
(2007/10/02)
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- MODIFICATION OF SINGLET CARBENE REACTIVITIES BY SOLVENT
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The solvent effect on the reactivity of singlet carbenes has been investigated.Competition reactions between pairs of alcohols for arylcarbenes in various solvents indicates that the O-H insertion selectivity is influenced only by 1,4-dioxane.Thus, phenylcarbene is some 33 times more reactive toward methanol relative to t-butyl alcohol in 90 molpercent dioxane than without solvent.Similar competition reactions between alcohol and olefin indicate that the O-H insertion-addition selectivities of arylcarbenes are considerably altered by dioxane.These results are interpreted as indicating that dioxane stabilizes singlet carbenes by complexing with its ione pairs of electrons.
- Tomoika, H.,Ozaki, Y.,Izawa, Y
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p. 4987 - 4994
(2007/10/02)
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- CONTROLLED OXIDATION OF BENZYL ETHERS ON IRRADIATED SEMICONDUCTOR POWDERS
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Irradiation of a suspension of powdered TiO2, a photoactive semiconductor, in oxygen saturated acetonitrile leads to mild selective oxidation of substrates containing a benzylic methylene by conversion of that carbon to a carbonyl group.The method is shown to be synthetically useful for the preparation of esters from ethers and ketones from hydrocarbons.A critical analysis of the products and of the possible intermediates results in a plausible mechanistic pathway for these photooxidations.
- Pincock, James A.,Pincock, Alexandra L.,Fox, Marye Anne
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p. 4107 - 4118
(2007/10/02)
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- NUCLEOPHILIC SUBSTITUTION OF ALKYL HALIDES BY ZINC SALTS-3 PREPARATION OF TERTARY ALKYL ESTERS AND ETHERS UNDER NON-SOLVOLYTIC CONDITIONS
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Zinc salts of carboxylic acids, phenols and alcohols are found to react with tertiary alkyl halides in nonpolar solvents and in presence of a base yielding the corresponding esters and ethers in moderate to good yields.
- Ravindranath, B.,Srinivas, P.
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p. 1623 - 1628
(2007/10/02)
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- Photochemical Transformations. 30. Photosolvolysis of Benzyl Chlorides in tert-Butyl Alcohol. 2. Nature of Excited States
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The photosolvolysis of a number of benzyl chlorides in tert-butyl alcohol, both as a result of direct irradiation and ketone triplet sensitization, has been studied.A variety of sensitization and quenching techniques have been used.The results obtained are rationalized by the assumption that there are two triplet states of the benzyl chlorides accessible in these experiments - one a short-lived upper state, which leads to solvolysis product, and another a long-lived (lower energy) state, which reverts to ground-state reactant.Consistent with this idea, m-methoxybenzyl chloride is shown to quench the photoreactions of benzopenone with benzhydrol without the formation of a significant amount of reactive species.The effects of wavelength on the reactions of p-acetobenzyl chloride are mesured and discussed in terms of the two-triplet concept.
- Cristol, Stanley J.,Bindel, Thomas H.
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p. 7287 - 7293
(2007/10/02)
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- The Mechanism of Photolysis of Benzyl Halides and Benzyl Acetate in Alcohols
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The photolysis of benzyl chloride, bromide, iodide, and acetate, and 3,5-dimethoxybenzyl bromide and acetate in methanol and t-butyl alcohol have been examined, and also 3,5-dimethoxybenzyl chloride in ethanol.Solvolysis products and products derived by non-ionic mechanisms are obtained by either direct photolysis at 254 nm or acetone-sensitised photolysis at 300 nm.The mechanisms of the reactions are discussed.
- Appleton, David C.,Brocklehurst, Brian,Kenna, James Mc,Kenna, Jean M. Mc,Thackeray, Stephen,Walley, Andrew R.
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- Photochemical Transformations. 26. Sensitized and Unsensitized Photoreactions of Some Benzyl Chlorides in tert-Butyl Alcohol
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Benzyl chloride and a variety of meta- and para-substituted derivatives have been irradiated in tert-butylalcohol at 254 nm or in acetone-tert-butyl alcohol mixtures at 300 nm.Quantum and chemical yields of photosolvolysis products (benzyl tert-butyl ether and/or benzyl alcohol), photohomolysis products (bibenzyl and 4-phenyl-2-methyl-2-butanol), and corresponding products from substituted benzylchlorides have been measured as functions of substrate concentration and medium composition.Sensitized reactions favor bond heterolysis, but direct irradiations favor homolysis, although reactions are not clean in either case.There is no correlation between quantum yields for photosolvolysis and Hammett ? or Brown ?+ constants, and no salt effects of added lithium perchlorate were observed, in either direct or sensitized reactions.
- Cristol, Stanley J.,Bindel, Thomas H.
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p. 951 - 957
(2007/10/02)
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- The Mechanism of Photolysis of Some Benzyltrimethylammonium Salts in Water and in Alcohols
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Photolysis of a range of benzyltrimethylammonium and 3,5-dimethoxybenzyltimethylammonium salts in water or methanol at 253.7 nm gave typically benzyl alcohols (or benzyl methyl ethers), toluenes, bibenzyls and isomers, and di- and tri-methylammonium salts.By detailed sensitisation and quenching experiments it was established that, in the photolysis of benzyltrimethylammonium bromide in aqueous t-butyl alcohol, benzyl t-butyl ether, benzyl alcohol, and some toluene were produced by a singlet pathway and bibenzyl by a triplet pathway.A general mechanistic scheme for all the photolyses studied is thus suggested.
- Appleton, David C.,Bull, David C.,Givens, Richard S.,Lillis, Veronica,Kenna, James Mc,et al.
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- Chemistry of the 2-Pinanols. 2. Investigation of the Utility of the Enhanced Basicities of the Pinanoxide Bases
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The utility of the alkoxides of cis- and trans-2-pinanol has been investigated.Yiels comparable to and exceeding those obtained with tert-butoxide are reported for the alkylation of ethyl acetoacetate, for the conversion of α-pinene oxide to trans-pinocarveol and cis-3-pinen-2-ol, and for the isomerization of vinylnorbornene and limonene.Dehydrohalogenation was effected rapidly on bornyl chloride and 2,6-dichlorocamphane-compounds reported to be inert to potassium tert-butoxide in tert-butyl alcohol.Reactions with 1-octyl bromide and with benzyl chloride showed that the pinanoxides have nucleophilicities comparable to that of tert-butoxide.
- Traynor, Sean G.,Kane, Bernard J.,Coleman, Jacquelyn B.,Cardenas, Carlos G.
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p. 900 - 906
(2007/10/02)
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