The synthesis of several 3,4-dihydro-4-oxo-2H-1,3-benzoxazine-carboxylic acids is described. The acids resulted from hydrogen carbonate hydrolysis of their corresponding esters which were prepared by condensation of salicylamide with various aldehydes and ketones. The use of certain aromatic aldehydes and ketones containing an ortho-carboxy-function led to isoindolobenzoxazine structures.