The mechanism of the cyclization of ?-(2-carboxyaryl)aminopropionic acids to 1,2,3,4-tetrahydro-4-oxoquinolines

It is shown that cyclization of Β-(2-carboxyaryl) aminopropionic acids to 1,2,3,4-tetrahydro-4-oxoquinolines in the presence of acetic anhydride and alkali metal acetates proceeds via the intermediate formation of the N-acetyl derivative of the monopotassium salt of the starting acid, which undergoes further conversion into the cyclic mixed anhydride. The latter decomposes with loss of CO2 to give the corresponding 1,2, 3,4-tetrahydro-4-oxoquinoline.