Die Umsetzung von Carbonsäureestern mit Natrium in Gegenwart von Trimethylchlorsilan
12 September 2002 (online)
The reaction of carboxylic acid esters with sodium in inert solvents (Bouveault-Blanc condensation) in the presence of trimethylchlorosilane is reviewed. By the addition of trimethylchlorosilane, which reacts with basic by-products, the reaction mixture is kept neutral. This completely prevents base-catalyzed side reactions such as ß-eliminations and Claisen- or Dieckmann-condensations. Trimethylchlorosilane has no effect, however, on side reactions which proceed via free-radical mechanisms. By addition of trimethylchlorosilane, the yields obtained in known acyloin syntheses can be increased and the scope of the original procedure considerably extended. The reaction products - bis-siloxy-alkenes - are either isolated or converted into acyloins by acid hydrolysis or alcoholysis. In several syntheses, they can also be directly used as "potential acyloins". Unlike a number of the corresponding acyloins, the bis-siloxy-alkenes can be stored under non-hydrolytic conditions for extended periods of time without undergoing decomposition.