Cesium phenoxide

However, a careful study of the experimental data has led to some general trends. For instance, the nature of the final products depends heavily on the alkali cations used in the starting compounds sodium and lithium phenoxides reacting under similar experimental conditions yield the related salicylates as major products [18] (Scheme 5.1), whereas potassium, rubidium, and cesium phenoxides yield mixtures of 2-hydroxy-benzoic acid and 4-hydroxy-benzoic acid [1] (Scheme 5.2). As a rule of thumb, the yield of p-hydroxybenzoic acid generally increases with the increasing ionic radius of the alkali metal. Both, temperature and C02-pressure were also reported to be paramount in the selectivity of the carboxylation ... 

Another phenoxide activating approach published by Buchwald et al. [18] is based on the reaction of cesium phenoxides with aryl bromides or iodides in the presence of catalytic amounts of copper(I) triflate and ethyl acetate in refluxing toluene (Scheme 3b). In certain cases equimolar amounts of 1-naphthoic acid have been added in order to increase the reactivity of the phenoxide. The authors assume the formation of a cuprate-like intermediate of the structure [(ArO)2Cu] Cs+ as the reactive species. In addition, diaryl ether formation between phenols and aryl halides has been achieved using a phosphazene base forming naked phenoxide in the presence of copper bromide in refluxing toluene or 1,4-dioxane [19]. 

Nucleophilic substitution of halogen by the S j l mechanism follows a related radical chain pathway (Scheme 3), in which the aryl radical Ar attacks a nucleophile Nm rather than abstracting hydrogen. The solvent should not contain easily abstractable hydrogen atoms in order to depress photodehaloge-nation. Halo-2-pyridones were also found to undergo nucleophilic substitution via an S,y.jl mechanism when reacted with cesium phenoxides, yielding hydroxyphenyl-2-pyridones. ... 

Higuchi, H., Hattori, M., and Ohmiya, S., Direct arylation of 2-pyridones photostimulated SRNl reaction between cesium phenoxides and chloro-2-pyridones. Heterocycles, 52, 253-260, 2000. Grabner, G., Richard, C., and Koehler, G., Formation and reactivity of 4-oxocyclohexa-2,5-di-enylidene in the photolysis of 4-chlorophenol in aqueous solution at ambient temperature, /. Am. Chem. Soc., 116, 11470-114780, 1994. 

ALDOL CONDENSATION Cesium fluoride. Dialkylboron trifluoromethane-sulfonates. Dichlorobis(cyclopentadi-enyl)zirconium. Diisobutylaluminum phenoxide. 2,5-Dimethylphenylpropi-onate. DimetIiyl(phenyllhio)aIuminum. Lithium iodide. Triethylborane. Tri-methylsilyl trifluoromethanesulfonate. Triphenyltin chloride. TrisCdiethyI-amino)sulfonium difluorotrimethyl-siliconate. 

The mechanism of the Kolbe-Schmitt reaction was investigated since the late 1800s, but the mechanism of the carboxylation could not be elucidated for more than 100 years. For a long time, the accepted mechanism was that the carbon dioxide initially forms an alkali metal phenoxide-C02 complex, which is then converted to the aromatic carboxylate at elevated temperature. The detailed mechanistic study conducted by Y. Kosugi et al. revealed that this complex is actually not an intermediate in the reaction, since the carefully prepared phenoxide-C02 complex started to decompose to afford phenoxide above 90 °C. They also demonstrated that the carboxylated products were thermally stable even at around 200 °C. The CO2 electrophile attacks the ring directly to afford the corresponding ortho- or para-substituted products. (When the counterion is large (e.g., cesium) the attack of CO2 at the ortho-position is hindered therefore, the para-substituted product is the major product.)... 

Diaryl ethers. Phenols and activated or unactivated aryl bromides and iodides react under the influence of Cu(OTf)j-benzene complex to give the ethers in refluxing toluene (19 examples, 76-93%). Cesium carbonate is used as base. When present as an additive, 1-naphthoic acid extends the generality of the method to less soluble phenoxides. 

A significantly more convenient method for the preparation of hydroxy acids was disclosed by Marasse in which a phenol is combined with an excess of an anhydrous carbonate salt at elevated temperature and pressure. The reaction is limited to potassium, rubidium, and cesium carbonate, yet avoids the stepwise preparation of anhydrous phenoxide salts. Recently, aqueous conditions have also been disclosed, which obviate the... 

Preparation of cyclic oligo(ether sulfone)s by cesium fluoride-catalyzed depolymerisation in aprotic solvents was reported by Colquhoun et al. [36, 37]. The fluoride ion cleaves the C-O bonds at temperatures > 140 °C and the resulting phenoxide ions attack the neighboring ether groups forming cyclics by backbiting . Several cyclic oligoethers up to the pentamer were isolated and characterized by X-ray crystal structure analyses. 

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