Chemo- and diastereoselective epoxidation of allylic alcohols with a titania–silica aerogel

Abstract

An amorphous mesoporous titania–silica aerogel (20 wt.% TiO 2–80 wt.% SiO 2) and tert-butylhydroperoxide have been used for the epoxidation of various allylic alcohols. Cyclic allylic alcohols and alkenols possessing an internal double bond were more reactive than the allylic alcohols with a terminal CC bond. Epoxide selectivities could be improved by catalyst pre-drying and hydrophobisation in toluene, as well as by the addition of (basic) zeolite 4Å and NaHCO 3 to the reaction mixture. Diastereoselective epoxidation of cyclic allylic alcohols yielded preferentially the cis-epoxides. The performance of the titania–silica aerogel in the epoxidation of allylic alcohols and α-β-unsaturated carbonyl compounds was compared to those of titania-on-silica and TS-1. Interestingly, titania-on-silica and TS-1 were inactive in the epoxidation of α-β-unsaturated carbonyl compounds.