Ring closure and rearrangement reactions of 4‐azido‐2‐oxoquinoline‐3‐carboxylates and 4‐azidocoumarin‐3‐carboxylates

Abstract

Abstract 4‐Azido‐2‐oxoquinoline‐3‐carboxylates and 4‐azidocoumarin‐3‐carboxylates 6 , which were obtained from the corresponding 4‐hydroxy derivatives 1 via 4‐tosylates 2 or 4‐chloro compounds 4 , cyclized upon thermolysis to 3‐alkoxyisoxazolo[4,3‐ c ]quinolin‐4(5 H )‐ones or the corresponding coumarins 8 , whereas at slightly higher temperatures a 3‐ O , 4‐ O ‐rearrangement took place to give the 4‐alkoxy‐isoxazolo[4,3‐ c ]‐quinolin‐3‐ones and the corresponding coumarins 9. The necessary reaction conditions could be obtained easily with the help of differential scanning calorimetry.