First examples of proline-catalyzed domino Knoevenagel/hetero-Diels-Alder/elimination reactions

A novel and efficient one-pot synthesis of lactones (pyranones) has been achieved by domino Knoevenagel/hetero-Diels-Alder/elimination reactions of O- and N-prenyl aldehyde derivatives with Meldrum's acid in the presence Of (L)- or (D),(L)-proline. The reaction proceeds cleanly at room temperature to afford cis- or trans-fused products in good yields with high diastereoselectivity.