A Cinchona Alkaloid-Functionalized Mesostructured Silica for Construction of Enriched Chiral β-Trifluoromethyl-β-Hydroxy Ketones over An Epoxidation-Relay Reduction Process.

Abstract

A cinchona alkaloid-functionalized heterogeneous catalyst is prepared through a thiol-ene click reaction of chiral N-(3,5-ditrifluoromethylbenzyl)quininium bromide and a mesostructured silica, which is obtained by co-condensation of 1,2-bis(triethoxysilyl)ethane and 3-(triethoxysilyl)propane-1-thiol. Structural analyses and characterizations disclose its well-defined chiral single-site active center, and electron microscopy images reveal its monodisperse property. As a heterogenous catalyst, it enables an efficient asymmetric epoxidation of achiral β-trifluoromethyl-β,β-disubstituted enones, the obtained chiral products can then be converted easily into enriched chiral β-trifluoromethyl-β-hydroxy ketones through a sequential epoxidation-relay reduction process. Furthermore, such a heterogeneous catalyst can be recovered conveniently and reused in asymmetric epoxidation of 4,4,4-trifluoro-1,3-diphenylbut-2-enone, showing an attractive feature in a practical construction of enriched chiral β-CF3 -substituted molecules.