Regioselective synthesis of 1 H,3 H,6 H[2]benzopyrano[4,3- d]pyrimidine-2,4-diones and 12 H-benzopyrano[3,2- c][1]benzopyran-5-ones by radical cyclization

Abstract

5-Hydroxy uracils or 4-hydroxy[1]benzopyran-2-ones were refluxed with 2-bromobenzyl bromides in acetone in the presence of anhydrous potassium carbonate to afford a number of 5-(2′-bromobenzyloxy) pyrimidine-2,4-dione (80–92%) or 4-(2′-bromobenzyloxy) benzopyran-7-ones (70–82%) respectively. These were then refluxed with tri- n-butyltin chloride and sodium cyanoborohydride in the presence of a catalytic amount of azobisisobutyronitrile (AIBN) for 3–4 h to give 1 H,3 H,6 H [2]benzopyrano[4,3- d]pyrimidine-2,4-diones (75–85%) or 12 H-benzopyrano[3,2- c][1]benzopyran-5-ones (70–85%) respectively.