Phenols, trifluoromethanesulfonic anhydride

Apart from aryl halides, other very easily available substrates for nickel-catalysed biaryl (II) synthesis are aryl sulfonates (XII). Method D is very efficient in the homocoupling reactions of substituted aryl sulfonates in good to excellent yields [15], Table 6. Substituted aryl sulfonates are readily obtained from phenols and trifluoromethanesulfonic anhydride, benzenesulfonyl-, tosyl- or methanesulfonyl chloride in pyridine, or in a suitable inert solvent such as dichloromethane in the presence of triethylamine or Hiinig s base. Among other nickel complexes, Ni(dppe)Cl2 and Ni(dppf)Cl2 have been used (10 mo1%) as slightly less versatile catalysts for the homo-couplings of naphthyl sulfonates in refluxing THF, DMF or their mixtures [42]. 

Other Uses. Imidazole is one of the best catalysts for the preparation of acid chlorides from the corresponding carboxylic acids and phosgene. Aryl triflates can be obtained from phenols, or better phenolates, using Trifluoromethanesulfonic Anhydride in combination with imidazole A-triflylimidazole is the reactive species. Photochemical deconjugations of enones can be erratic but are promoted by the presence of a weak base such as imidazole or pyridine in polar solvents. ... 

A,iV-DIMETHYLMETHANIDE (68-12-2) Forms explosive mixture with air (flash point 136°F/58 C). Violent reaction with nitrates, carbon tetrachloride, hexachlorocyclohexane, and other halogenated compounds, particularly in contact with iron or strong oxidizers, may cause fire and explosions. Vigorous reaction with alkylaluminums. Incompatible strong acids, allyl trifluoromethanesulfonates, ammonia, chlorinated hydrocarbons, cresols, chromic anhydride, isocyanates, nitrates, phenols, magnesium nitrate, methylene diisocyante, phosphorous trioxide, triethyl aluminum. Attacks some plastics and coatings. 

Reaction with Alcohols and Phenols. The reaction of alcohols and phenols with triflic anhydride (Tf20) at 0°C in the presence of a base (usually Pyridine) in an inert solvent (usually dichloromethane) for 2-24 h affords the corresponding reactive trifluoromethanesulfonate esters (triflates). When triflic anhydride and pyridine are combined, the pyridinium salt forms immediately and normally precipitates out from the reaction mixture. Nevertheless, the salt is an effective esterifying agent, reacting with the added alcohol to give triflates in high yields (eq 1). ... 

---