Oxidation–Isomerization of an Olefin to Allylic Alcohol Using Titania–Silica and a Base Co-catalyst

The potential of a two-step, one-pot synthesis of α,β-unsaturated alcohols from olefins is illustrated on the example of 4-hydroxy-isophorone using titania–silica aerogels and basic co-catalysts. Kinetic analysis of the complex reaction network revealed that titania–silica is efficient in the epoxidation of β-isophorone (3,5,5-trimethyl-3-cyclohexen-1-one) with TBHP at 353 K, whereas the acid/base-catalyzed in situ rearrangement to 4-hydroxy-isophorone (4-hydroxy-3,5,5-trimethyl-cyclohex-2-enone) is slow. Addition of solid bases such as CaO, Na2CO3, and KF/CaF2 remarkably accelerated the rearrangement and up to 77.5% selectivity at 83% conversion was achieved in 3 h. Stronger bases (K2CO3, BaO, Mg–Al–O-tBu, guanidine bases) inhibited the epoxidation reaction due to deactivation of the isolated Ti sites, and favored isomerization of β-isophorone to α-isophorone. Hydrophobization of titania–silica by covalently bound surface phenyl groups greatly suppressed oligomerization and isomerization of β-isophorone but did not improve the selectivity to 4-hydroxy-isophorone.