High chemoselectivity in microwave accelerated intramolecular domino Knoevenagel hetero Diels-Alder reactions - an efficient synthesis of pyrano[3-2c]coumarin frameworks

4-Hydroxy coumarin and its benzo-analogues undergo intramolecular domino Knoevenagel hetero Diels-Alder reactions with O-prenylated aromatic aldehydes and the aliphatic aldehyde, citronellal to afford pyrano fused polycyclic frameworks. A high degree of chemoselectivity was achieved by the application of microwave irradiation. (C) 2002 Elsevier Science Ltd. All rights reserved.