Mechanistic Study of Oxidative Thiolester Formation in Cationic Vesicles - The Effect of pH and Reaction Field -

Abstract

We succeeded to construct a reaction system mimicking the function of the pyruvate dehydrogenase complex and obtained thiolesters in good yields from benzaldehydes in dichloromethane. The key step of the formation was the attack of the thiazolium carbene to the formyl group. On the basis of the above findings, we have set up a reaction system in which thiolester is formed within a vesicular membrane composed of dimethyldimyristylammonium bromide, 3-dodecyl-4-methyl-thiazolium bromide (catalyst), and N¹-dodecylnicotinamide bromide (oxidant) in a ratio of 0.8 mM : 0.6 mM : 0.3 mM, in a triethanolamine-HCl buffer (30 mM, pH ~ 7.7) solution. In the vesicle, 4-methoxycarbonylbenzaldehyde was converted to the corresponding thiolester in about 70% yield. As the yield depends on the amount of the catalyst and pH, the reaction efficiency may be influenced by the competitive nucleophilic attack to the formyl group by hydroxide anion.