Metal cation-exchanged montmorillonite(Mn+-Mont)-catalysed carbonyl-ene reactions

Abstract

Metal cation-exchanged montmorillonite (M ⁿ⁺ -mont) works in acetonitrile at 80 °C as a Lewis acid catalyst for the intermolecular carbonyl-ene reaction of α-methylstyrenes with paraformaldehyde to give the corresponding homoallylic alcohols, Zr ⁴⁺ -mont being the most effective of the many M ⁿ⁺ -mont catalysts examined. Similarly, the catalyst is also useful for the highly stereoselective intramolecular cyclization of citronellals to afford isopulegols, the reaction being much faster. Regeneration of the catalyst is confirmed for Zr ⁴⁺ -mont, which can be effectively recycled at least five times.