First asymmetric Diels-Alder reactions of furan and chiral acrylates. Usefulness of acid heterogeneous catalysts

TiCl4 and ZnCl2 supported on silica gel catalyze the reactions of furan with methyl, (1R,2S,5R)-menthyl, and (1R,2S,5R)-8-phenylmenthyl acrylates. The best results are obtained when reactions are carried out without a solvent. The endo/exo and diastereofacial selectivities depend on the nature of the catalyst and on the reaction conditions. With the (1R,2S,5R)-menthyl acrylate 44% de in endo cycloadducts and 20% de in exo cycloadducts are the best asymmetric inductions. With the (1R,2S,5R)-8-phenylmenthyl acrylate 68% de in endo and 70% de in exo cycloadducts are obtained.This work was made possible by the generous financial support of the Comisión Interministerial de Ciencia y Tecnología (project MAT96-1053-C02-01). One of us (E.P.) thanks the Diputación General de Aragón for a grant.Peer reviewe