Selective reactions of terpenes, catalyzed by different heterogeneous systems, are reported. α-pinene and limonene epoxides can be effectively isomerized to carbonyl compounds (selectivity >70%) over silica aluminas that appear to be good alternatives to homogeneous ZnBr2. The different reactivity of geometric isomers can be used to separate them. Unsaturated ketones can be converted through a two-step one-pot reaction in cyclic or bicyclic ethers through a bifunctional process involving a hydrogenation and an acid-catalyzed step. However, the choice of the solvent allows to inhibit the acidic sites, thus obtaining a selective hydrogenation reaction. On the other hand, the acidic reaction alone can be useful for alcohol epimerization and epimer separation. Grafting of Ti in a siliceous matrix gives rise to a material with both redox and acidic properties. Solids obtained in this way are active and selective in the epoxidation of terpenic alcohols but can also promote bifunctional reactions.

Mono- and Bifunctional Heterogeneous Catalytic Transformation of Terpenes and Terpenoids

Ethyl valerate and pentyl valerate, suitable as a gasoline additive and diesel component respectively, can be obtained in a one pot one step reaction from γ-valerolactone, readily available from lignocellulosic biomass. The reaction takes place in ethanol under H2 through nucleophilic addition of the alcohol to the carboxylic group giving hydroxypentanoate, dehydration to pentenoate and hydrogenation to the saturated ester. The bifunctional catalyst used consists of a non noble metal, namely copper, supported on an amorphous weakly acidic material, therefore representing an interesting alternative to Pt–zeolite catalysts. Pentyl valerate can be obtained in one pot with conversions >90% and selectivity up to 83%.

New generation biofuels: γ-valerolactone into valeric esters in one pot

Heterogeneous Cu-catalysts for the reductive deoxygenation of aromatic ketones without additives

The one-step transformation of (+)-citronellal into (-)-menthol has been realised with yield ∼90% and stereoselectivity up to 80% under mild conditions in the presence of Cu/SiO2 by exploiting the presence of acidic and hydrogenation sites on the catalyst surface, the unusual reducibility of an olefinic bond under these conditions and the chemoselectivity of the process.

Bifunctional copper catalysts. Part II. Stereoselective synthesis of (-)-menthol starting from (+)-citronellal

Chlorosulfonic acid as a convenient electrophilic olefin cyclization agent

Bifunctional copper catalysts. A one step synthesis of bicyclic ethers starting from α,β-unsaturated ketones

A new, one pot synthesis of bicyclic ethers starting from α,β-unsaturated ketones containing an additional isolated olefinic bond is proposed. It relies on highly chemoselective hydrogenation of the enone group to the corresponding alcohol in the presence of supported copper catalysts, and on the presence of acidic sites on the catalyst support activating the double bond as a carbocation.

Vincenzo Leo

Papers

Bifunctional copper catalysts. A one step synthesis of bicyclic ethers starting from α,β-unsaturated ketones

Bifunctional Copper Catalysts. A One Step Synthesis of Bicyclic Ethers Starting from α,β-Unsaturated Ketones.