Unusual reduction of a lactone carbonyl in a Bu3SnCl and Na(CN)BH3 mediated radical cyclization of 3-(o-bromophenoxymethyl)coumarins

3-Chloromethyl coumarin was treated with different substituted 2-bromophenols in the presence of anhydrous potassium carbonate in refluxing acetone to afford a number of 3-(2-bromophenoxymethyl)coumarins 3a–f in 80–95% yield. These were then refluxed with tributyltin chloride and sodium cyanoborohydride in benzene under nitrogen, in the presence of a catalytic amount of azobisisobutyronitrile (AIBN) for 7–10 h to give spiro[chroman-3,3′-(2′H)-benzofurans] 4a–f in 60–75% yields.