Phase transfer catalysis: some recent applications in organic synthesis

A survey dealing with the use of anhydrous potassium carbonate as an efficient base for promoting organic reactions under solid-liquid phase transfer catalysis (SL-PTC) conditions is reported. In particular, the generation in situ of trifluoro- and trichloroacetamidide, and reactions of these azaanions with 2-bromocarboxylic esters and epoxides, affording protected alpha-amino acids and beta-amido alcohols, respectively, are described. The reduction of allylic nitroderivatives with CS2 to oximes or nitriles under SL- and liquid-liquid PTC (LL-PTC) is also presented. Finally, new preparation methods and a study of the reactivity of quaternary onium fluorides, hydrogendifluorides and dihydrogentrifluorides, together with the use of dihydrogentrifluorides as hydrofluorinating agents under SL-PTC conditions, are reported. (C) 1999 Elsevier Science B.V. All rights reserved.