Water-resistant Lewis-acid sites: carbonyl-ene reactions catalyzed by tin-containing, hydrophobic molecular sieves

Two solid Lewis acids, namely Sn-Beta and Sn-MCM-41, have been applied to the Carbonyl-Ene reaction of β-pinene and α-methylstyrene with paraformaldehyde.For the more bulky molecule β-pinene the mesoporous material Sn-MCM-41 has been found to be the better catalyst whereas for the smaller α-methylstyrene Sn-Beta has shown a higher activity.Best selectivities have been observed in nitrile solvents, such as acetonitrile and butyronitrile, whereas reactions in toluene or dioxane have been less selective.The catalysts are water resistant what has been evidenced by addition of up to 200 wt% (with respect to the catalyst) of water without loss of activity or selectivity.Sn-MCM-41 has been employed in several cycles with intermediate regeneration, always recovering the high activity.