- Masked N-Heterocyclic Carbene-Catalyzed Alkylation of Phenols with Organic Carbonates
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An easily prepared masked N-heterocyclic carbene, 1,3-dimethylimidazolium-2-carboxylate (DMI-CO2), was investigated as a “green” and inexpensive organocatalyst for the alkylation of phenols. The process made use of various low-toxicity and renewable alkylating agents, such as dimethyl- and diethyl carbonate, in a focused microwave reactor. DMI-CO2 was found to be a very active catalyst and excellent yields of a range of aryl alkyl ethers were obtained under relatively benign conditions. The observed difference in the conversion behavior of phenol methylation, in the presence of either the carbene or 1,8-diazabicycloundec-7-ene (DBU) catalyst, was rationalized on the basis of mechanistic investigations. The primary mode of action for the N-heterocyclic carbene is nucleophilic catalysis. Activation of the dialkyl carbonate electrophile results in concomitant evolution of an organo-soluble alkoxide, which deprotonates the phenolic starting material. In contrast, DBU is initially protonated by the phenol and thus consumed. Subsequent regeneration and participation in nucleophilic catalysis only becomes significant after some phenolate alkylation occurs.
- Lui, Matthew Y.,Yuen, Alexander K. L.,Masters, Anthony F.,Maschmeyer, Thomas
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p. 2312 - 2316
(2016/10/24)
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- Synthesis of 2,6-disubstituted and 2,3,6-trisubstituted anilines
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A number of 2,6-disubstituted and 2,3,6-trisubstituted anilines have been prepared via the selective para dehalogenation of the corresponding anilines. Modification of the substituents on the amino nitrogen demonstrates that the selectivity is derived from steric rather than electronic effects. The effects of the choice of formate hydrogen donor, Pd catalyst, solvent, and temperature upon the efficiency and selectivity of the dehalogenation are discussed.
- Pews,Hunter,Wehrmeyer
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p. 4809 - 4820
(2007/10/02)
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- A safe and economical synthesis of 3-(trifluoromethoxy) aniline from 2-chlorophenol
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A simple, safe and realistic synthesis of 3-(trifluoromethoxy) aniline from 2-chlorophenol is proposed, the key step being a regiospecific arynic amination of 2-chloro (trifluoromethoxy) benzene.This method has been extended to the synthesis of 4-chloro-3-(trifluoromethoxy) aniline from 2,6-dichlorophenol.Some unusual products are obtained during the reaction between sodium amide and 2-chloro (chlorodifluoromethoxy) benzene, the formation of which is discussed.
- Langlois, Bernard,Soula, Gerard
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p. 925 - 929
(2007/10/02)
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- Tris(polyoxaalkyl)amines (Trident), a New Class of Solid-Liquid Phase-Transfer Catalysts
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A new class of solid-liquid phase-transfer catalysts has been prepared.These tris(polyoxaalkyl)amines (I) are designed to obtain the best balance between straightforward synthesis (cheap starting materials), high activity, easy recovery, and low toxicity.The catalysts are synthesized from ethylene glycols by a simple one-step method in yields in the range of 65-81percent.They show high catalytic effects in aliphatic nucleophic substitutions and aromatic nucleophilic substitutions on activated and unactivated molecules.In the Ullman synthesis (a new PTC reaction) there is a synergic effect of anionic activation by tridents and by copper salts.Reactions have been carried out at temperatures up to 180 deg C without evidence of decomposition of the tris(polyoxaalkyl)amines. The behavior and catalytic activity of these catalysts are discussed.
- Soula, Gerard
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p. 3717 - 3721
(2007/10/02)
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- THE REACTIONS OF UNACTIVATED ARYL HALIDES WITH SODIUM METHOXIDE IN HMPA; SYNTHESIS OF PHENOLS, ANISOLES, AND METHOXYPHENOLS
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Sodium methoxide reacts with dichlorobenzenes in HMPA to give the chloroanisoles as a result of a SNAr process.Excess MeONa then effects the demethylation of the ethers to give the chlorophenols via an SN2 reaction.With tri- and tetrachlorobenzenes the initially formed chloroanisoles can be dealkylated to chlorophenols or can suffer further substitution to give the chlorodimethoxybenzenes; these react with excess MeONa to give the chloromethoxyphenols.The results obtained with the various isomers of the di-, tri-, and tetrachlorobenzenes are presented and discussed on the basis of the electronic effects of the substituents.
- Testaferri, L.,Tiecco, M.,Tingoli, M.,Chianelli, D.,Montanucci, M.
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p. 193 - 198
(2007/10/02)
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- Nucleophilic Displacement in Polyhalogenoaromatic Compounds. Part 11. Kinetics of Protiodeiodination of Iodoarenes in Dimethyl Sulphoxide-Methanol
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The rates of methoxide-ion induced protiodeiodination of a number of polychloroiodobenzenes and their derivatives have been measured in dimethyl sulphoxide-methanol (9:1 v/v; 323.2 K).The true reagent under these conditions appears to be the dimethyl sulphoxide anion, and the rates of reaction in some cases appear to approach that expected of a diffusion controlled process.This corresponds to a major decrease in the efficacy of further activating substituents in the aromatic system, altough deactivating groups such as p-OMe still show large effects.Chlorine promotes protiodeiodination in the order of efficiency o-Cl > m-Cl > p-Cl; the trifluoromethyl group activates displacement in the order o-CF3 > p-CF3 > m-CF3, although with much less difference between isomeric sites. o-Nitro-groups promote protiodeiodination whereas the p-nitro-group encourages methoxydeiodination.No evidence of methoxydeiodination was found in attack of the polychloroiodobenzenes, although the rates of methoxydechlorination of the corresponding polychlorobenzenes suggest that in some cases this might occur.Evidence rejecting the possible SRN1 mechanism and supporting nucleophilic attack by a carbanionic species upon iodine is presented.
- Bolton, Roger,Moore, Clive,Sandall, John P.B.
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p. 1593 - 1598
(2007/10/02)
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- Formation of Nonaromatic Products in the Chlorination of Simple Substituted Aromatic Ethers
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The neat chlorination of 4-chloroanisole produces 1,3,4,5,6-pentachloro-4-methoxycyclohexene in 35percent yield.Mono- and dichlorinated anisoles and a variety of simple substituted anisoles were chlorinated to determine the generality of nonaromatic product formation. 3,4-Dichloroanisole, 4-fluoroanisole, 4-bromoanisole, 4-methylanisole, and 4-chlorophenetole form similar products based on their spectral properties.These products are proposed to form by a cis-1,2-chlorine addition followed by rapid cis-1,4 chlorine addition.On the basis of the NMR data, a predominate configuration is proposed.
- Watson, William David
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p. 5270 - 5276
(2007/10/02)
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