Triflate with carboxylic acid salts

An alternative solution to the limitations of the aryl carboxylate salts mentioned previously is a new bimetalhc catalyst system that allows the replacement of aryl hahdes by aryl triflates [14, 67]. The reaction proceeds efficiently with Pdl, Tol-BINAP, Cu O, and 1,10-phenanthroline, affording the corresponding unsymmetrical biaryls (Scheme 22.47). It is noteworthy that the reaction is generally applicable to aromatic carboxylic acid salts, regardless of their substitution pattern. The use of microwave irradiation has proved beneficial for this ARCIS reaction, since under these conditions the Pd(ll) catalyst is almost instantaneously reduced to Pd(0) [68]. Similarly, substituted aryl tosylates have been found to be suitable substrates in decarboxylative couphng reactions with a fuU range of benzoic acids (Scheme 22.47) [69]. 

Polymer-supported triphenylphosphine ditriflate (37) has been prepared by treatment of polymer bound (polystyrene-2% divinylbenzene copolymer resin) triphenylphosphine oxide (36) with triflic anhydride in dichloromethane, the structure being confirmed by gel-phase 31P NMR [54, 55] (Scheme 7.12). This reagent is effective in various dehydration reactions such as ester (from primary and secondary alcohols) and amide formation in the presence of diisopropylethylamine as base, the polymer-supported triphenylphosphine oxide being recovered after the coupling reaction and reused. Interestingly, with amide formation, the reactive acyloxyphosphonium salt was preformed by addition of the carboxylic acid to 37 prior to addition of the corresponding amine. This order of addition ensured that the amine did not react competitively with 37 to form the unreactive polymer-sup-ported aminophosphonium triflate. 

The direct condensation of carboxylic acids with aliphatic alcohols has been investigated by the use of fluorous ammonium salts as metal-free catalysts (Equation 4.24). Esterification reactions were carried out under mild fluorous biphasic conditions, in the presence of 1 mol% of fluorous ammonium triflate and without any water removal techniques. In the case of primary and secondary aliphatic alcohols, good to excellent ester yields were obtained. The fluorous ammonium triflate salt was easily recovered by simple phase separation and reused at least three times without any significant loss of activity [45],... 

Other nucleophiles react with equal facility with 189 [72] (Scheme 28). Phenols furnish (/ )-2-aryloxypropionates (199) in high yield. Even protected sugar derivatives displace the triflate group to afford muramic acid analogs [73]. Potassium salts of alkyl or aryl carboxylic acids produce (i )-lactates (200) and mercaptans give (i )-thiolactates (201) [72]. 

Besides the traditional coupling between alkenes and aryl (vinyl) halides, other functionalized aryl derivatives can also couple with alkenes in the Heck reaction, including aryl silanes,stannanes, bismuth, antimony,triflates, boric acid, phosphonic acid, carboxylic acid, and diazonium salt. ... 

Feringa and coworkers reported a copper-catalyzed O-arylation of dialkyl phosphonates and phosphoramidates with diaryliodonium triflates and 2,6-di-ferf-butylpyridine (DTBP), giving easy access to mixed alkyl aryl phosphonates via elimination of one of the alkyl groups as the alkyl triflate prior to arylation (Scheme 10a) [133]. Aryl(mesityl)iodonium salts reacted in a chemoselective way. Copper-catalyzed arylations of hydroxamic acids [134] and carboxylic acids [135] have also been reported, the latter utilizing thiophosphoramides as cooperative catalysts to allow arylation at room temperature. Onomura s group discovered a Cu-catalyzed monoarylation of vicinal diols in toluene at 100 °C. Only traces of product were obtained with alcohols lacking the vicinal hydroxyl group [136]. 

A mixture of phenylacetic acid, benzyl alcohol, and tri-n-butylamine in methylene chloride added under argon to a mixture of l-methyl-2-bromopyridinium iodide and methylene chloride, and refluxed 3 hrs. benzyl phenylacetate. Y 97%. F. e., also with l-methyl-2-chloropyridinium iodide, s. T. Mukaiyama et al., Chem. Lett. 1975, 1045 Bull. Chem. Soc. Japan 50, 1863 (1977) carboxylic acid amides from amines (cf. Synth. Meth. 26, 367) s. ibid. 1975, 1163 3,4-dihydro-2H-pyrido-[1,2-a]pyrimid-2-one as acid scavenger cf. ibid. 1976, 13, 57 lactones from hydroxycarboxylic acids (cf. Synth. Meth. 17, 320) with 2-chloropyridine methio-dide and triethylamine s. ibid. 1976, 49 esters with 2 halogeno-3-ethylbenzothia-zolium salts of ibid. 1976, 267 2-chloro-N-methylbenzothiazolium triflate as condensing agent s. F. Souto-Bachiller, G. S. Bates, and S. Masamune, Chem. Com-mun. 1976, 719. 

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