Heterogeneous activation of Diels-Alder reactions of non-chiral and chiral (E)-2-cyanocinnamates

Abstract

The Diels-Alder reactions of the non-chiral methyl (E)-2-cyanocinnamate and the chiral (E)-2-cyanocinnamates of (−)-menthol and of (R)-pantolactone with cyclopentadiene are carried out in the presence of several solids. Reactions are carried out with or without a solvent and the results are compared. With the three dienophiles, it is possible to reach high percentages of conversion with good endo/exo selectivities. (E)-2-cyanocinnamate of (−)-menthol leads to higher asymmetric inductions than (E)-2-cyanocinnamate of (R)-pantolactone. The comparison of these results with those obtained using AlEt2Cl or TiCl4 shows that the heterogeneous Lewis acids used in this work behave like homogeneous aluminium Lewis acids and none of them, even not those obtained from TiCl4, are able to form chelate complexes with suitable dienophiles.