Comprehensive Theoretical Investigation on the Regioselectivity in the Nucleophilic Ring Opening of Epoxides

Abstract

The regioselectivity in the ring opening of epoxides with various nucleophiles has been investigated in depth using quantum mechanical methods. Alkylepoxides are attacked regioselectively at their less substituted side, controlled by the steric effect, while aryl/alkenylepoxides show alterable regioselectivities, regulated by a combined action of the steric hindrance and the electronic effect of aryl and alkenyl groups, impacted by nucleophiles, solvents, and catalysts as well. That is, the steric repulsion of mono/dialkyl, electronwithdrawing aromatic groups, nucleophiles as hard bases, and nonpolar solvents make the ring-opening at their less substituted side predominantly, whereas electron-donating aryl substitutents, nucleophiles as soft bases, polar solvents, and acidic catalysts lead to the favored attack at their more substituted side. Aryl and alkenylepoxides prefers SN1 ring opening mechanism under the catalysis of strong acidic catalysts. Herein, a panorama has been drawn to provide a comprehensive insight into controlling the regioselectivity in the nucleophilic ring-opening of epoxides, and a general rule to predict the regioselectivity. Keywords: DFT study, epoxide, nucleophile, regioselectivity, ring opening