2006 Volume 64 Issue 6 Pages 651-663
More environmentally benign alternatives to current chemical processes, especially large-scale fundamental reactions, are highly desirable for many reactions. We have developed bulky diarylammonium pentafluorobenzenesulfonates 1a and 2a as mild and extremely active dehydration catalysts. In the presence of the catalysts, dehydrative cyclization of 1, 3, 5-triketones and ester condensation of carboxylic acids with equimolar amounts of alcohols are performed in heptane by heating at 80°C without the removal of water. We have also developed an efficient molybdenum oxide-catalyzed dehydrative cyclization of serine, threonine, and cysteine derivatives, which gives oxazolines and thiazolies. In the presence of molybdenum oxides, the reaction is carried out by heating at azeotropic reflux with the removal of water. Phosphate monoesters are synthesized from a mixture of phosphoric acid and alcohols in the presence of tributylamine. The reaction is promoted by nucleophilic bases such as N-butylimidazole. The hydroxyl groups of amino alcohols, such as 5'-hydroxyl group of 2', 3'-O-isopropylidene ribonucleosides, are phosphorylated selectively.
