Synthesis of Substituted Coumarins and 2‐Quinolinones by Cycloisomerisation of (Hydroxy/aminophenyl)propargyl Alcohols

Abstract A new cycloisomerization strategy for the synthesis of coumarins and quinolinones is described. The addition of ethoxyacetylide to 2‐hydroxyacetophenones directly resulted in 4‐substituted coumarins by 6‐ endo ‐ dig cycloisomerisation of the intermediate 3‐ethoxy‐1‐(2‐hydroxyphenyl)‐2‐propyn‐1‐ols. Under similar conditions, 2‐aminoacetophenone produced 2‐ethoxyquinoline, a masked quinolinone, which was converted into the quinolinone by acid treatment. N ‐Protected intermediate 8 was isolated and converted into the quinolinone [with In(OTf) 3 or H 2 SO 4 ] or the 3‐iodo‐2‐quinolinone (with I 2 and H + ).