Stereoselective intramolecular hetero Diels-Alder reactions of l-oxa-l,3-butadienes:a novel approach for the synthesis of complex annulated uracils

摘要

The intramolecular hetero Diels-Alder reactions of l-oxa-l,3-butadienes 4,obtained from salicylaldehyde 1 via O-allyl-ation followed by Knoevenagel condensation with barbituric acids 3 in the presence of hydrochloric acid as catalyst,affords the tetracyclic uracil derivatives 5 and 6 in a Stereoselective manner and high overall yields.