Acid-catalysed oxidative ring-opening of epoxide by DMSO. Theoretical investigation of the effect of acid catalysts and substituents
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DFT studies have been carried out in order to investigate the reaction mechanism of a series of acid-catalysed oxidative ring-opening of epoxides in DMSO. The role of the acid catalyst during the oxidation of ethylene oxide has been investigated by employing three acids, namely H3O+, Li+, and Mg2+. Effects of substituents on the epoxide have been investigated by including butene oxide and cyclopentene oxide as the reacting species. Stationary points have been obtained at the B3LYP/6–31++G(d,p) level of theory and the reaction barriers have been evaluated through free-energy calculations. This is the first mechanistic elucidation for such a process, involving oxidation of the epoxide ring by DMSO. The mechanism proceeds in two steps, namely a ring-opening step followed by an intramolecular proton transfer which leads to an α-hydroxyketol. The results show that the second step is the energetically less favourable, a feature consistent with the harsh experimental conditions needed to obtain such products. The role of the acid catalyst is discussed and we show that use of H3O+ or Mg2+ as an activator leads to similar results concerning the reaction energetics.
KeywordsDensity functional theory Epoxide Ring-opening Lewis acid-catalyst Reaction mechanisms
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J. Golebiowski and S. Antonczak seize the opportunity of this special issue to gratefully thank Pr. Jean-Louis Rivail for the great years spent in his laboratory.