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 ...
