HETEROGENEOUS ACTIVATION OF DIELS-ALDER REACTIONS OF NONCHIRAL AND CHIRAL (E)-2-CYANOCINNAMATES

The Diels-Alder reactions of the non-chiral methyl (E)-2-cyanocinnamat e and the chiral (E)-2-cyanocinnamates of(-)-menthol and of (R)-pantol actone with cyclopentadiene are carried out in the presence of several solids. Reactions are carried out with or without a solvent and the r esults are compared. With the three dienophiles, it is possible to rea ch high percentages of conversion with good endo/exo selectivities. (E )-2-cyanocinnamate of (-)-menthol leads to higher asymmetric induction s than (E)-2-cyanocinnamate of (R)-pantolactone. The comparison of the se results with those obtained using AlEt(2)Cl or TiCl4 shows that the heterogeneous Lewis acids used in this work behave like homogeneous a luminium Lewis acids and none of them, even not those obtained from Ti Cl4, are able to form chelate complexes with suitable dienophiles.