Use of different microporous and mesoporous materials as catalyst in the Diels-Alder and retro-Diels-Alder reaction between cyclopentadiene and p-benzoquinone activity of Al-, Ti- and Sn-doped silica

Diels-Alder cycloaddition between cyclopentadiene and p-benzoquinone has been studied using amorphous silica and different ITQ-2 and MCM-41 pure silica and metal containing materials as catalysts. The reaction can afford different products depending on the molecular reacting site. and the possibility of consecutive additions. Structured solid catalysts increase the selectivity to the endo-endo isomer. Silanol groups have not enough Bronsted acidity to interact with the carbonyl groups present in the dienophile. to reduce LUMO's energy and provide a better overlap between HOMO and LUMO. according to the frontier molecular orbital theory. The introduction of transition metal atoms in the framework increases the reaction rate for the Diels-Alder reaction while preserving the selectivity to the endo-endo isomer. The presence of more acidic OH groups enhance the retro-Diels-Alder reaction increasing (fie selectivity to the endo-exo isomer. (c) 2005 Elsevier B.V. All lights reserved.