CLAY-CATALYZED ASYMMETRIC DIELS-ALDER REACTION OF CYCLOPENTADIENE WITH CHIRAL ACRYLATES

Clay-catalysed Diels-Alder reactions of cyclopentadiene with several chiral acrylates are studied. The results obtained show that these solids are not efficient catalysts when chiral auxiliaries of large size are used. Clay-catalysed reactions between cyclopentadiene and (R)-O-acryloylpantolactone are compared with non-catalysed and TiCl4 and EtAlCl2-catalysed reactions. With regard to diastereofacial selectivity, the clays studied behave like homogeneous aluminium catalysts. Clay-catalysed reactions of (R)-O-acryloylpantolactone lead to the (1S,2S,4S,)-cycloadduct with good chemical yield, high % d.e. and excellent endo/exo selectivity. Given that (-)-menthyl acrylate leads to the (IR,2R,4R)-cycloadduct with about the same diastereofacial selectivity, (-)-menthol and (R)-pantolactone behave as complementary chiral auxiliaries.