CC bond formation by radical cyclization: Facile syntheses of [6,6]pyranothiopyrans and [6,6]pyridothiopyrans

Abstract

Abstract magnified image 4‐Chloromethylthiopyrano[3,2‐c][1]benzopyran‐5‐(2H)‐ones were refluxed with o‐bromophenols in acetone in the presence of anhydrous potassium carbonate and sodium iodide to afford a number of 4‐aryloxymethylthiopyrano[3,2‐c][1]benzopyan‐5‐(2H)‐ones in 72–79% yields. These compounds were refluxed with tri‐n‐butyltin hydride and azobisisobutyronitrile in dry benzene for 7–8 h to give [6,6]pyranothiopyrans in 76–84% yields with good diastereoselectivity. Similarly, [6,6]pyridothiopyrans were also synthesized in 70–75% yields with excellent diastereoselectivity. J. Heterocyclic Chem., (2009).