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 (5H)- 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 ...