日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Non-polar cyclopentadiene as well as polar formaldehyde and acrolein are known as labile molecules easy to polymerize. Once those labile molecules are adsorbed into the polar nano space of faujasite zeolites X and Y, it is confirmed by ¹³C MAS NMR and chemical transformation that the molecules can survive in a monomer form for a long period of time even at ambient temperatures. In addition, the adsorbed molecules are not only stably preserved in supercages of faujasite zeolites, but also activated enough to react with π-electronic nucleophiles such as simple olefins, indoles, anisole, methacrylonitrile, and unsaturated carbonyl compounds in the carbonyl-ene reaction, Friedel-Crafts-type alkylation, and Diels-Alder reaction. Interestingly, the reactivity of cyclopentadiene adsorbed in zeolite for the Diels-Alder reaction is critically influenced by its adsorption density in the supercage: Densely adsorbed cyclopentadiene gives Diels-Alder adducts in high yields, while poor results are obtained with sparsely trapped cyclopentadiene. We speculate that once hydrophobic molecules are densely accommodated inside polar hydrophilic supercages of the zeolite, the organic molecules cohere to increase "internal pressure", leading to acceleration in the Diels-Alder addition with a negative activation volume.