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

An amorphous mesoporous titania-silica aerogel (20 wt.% TiO2-80 wt.% SiO2) 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 4 Angstrom and NaHCO3 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 alpha-beta-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 alpha-beta-unsaturated carbonyl compounds. (C) 1999 Elsevier Science B.V. All rights reserved.