Catalytic epoxidation of olefins using MoO3 and TBHP: Effect of the addition of chiral 2-substituted pyridines on the catalytic rate and asymmetric induction

Attempts were made at epoxidising enantioselectively some simple olefins using MoO3 (0.17 mol%), TBHP and five different chiral non-racemic 2-substituted pyridine ligands. A maximum conversion of 88% using 4-methylstyrene, and a maximum selectivity of ≥98% using 1-methylcyclohexene and 1-phenylcyclohexene were obtained. All ligands screened showed the ability to accelerate the reaction. However, it was ligand 4, that was the quickest to do so and showed the greatest acceleration. The observation of a reaction rate acceleration in the presence of such ligands appeared to indicate the formation of a Mo(VI)oxoperoxy-ligand complex. In no case was asymmetric induction observed.

Graphical abstractAttempts were made at epoxidising enantioselectively some simple olefins using MoO3, TBHP and a variety of chiral non-racemic 2-substituted pyridine ligands. No asymmetric induction was observed despite evidence of ligand acceleration. A maximum conversion of 88% and a maximum selectivity of ≥98% were observed.Figure optionsDownload full-size imageDownload as PowerPoint slide