Reactions of anthranilamide with isocyanates: A new facile synthesis of 2,3‐dihydro‐5H‐oxazolo[2,3‐b]quinazolin‐5‐one and 3,4‐dihydro‐2H,6H‐[1,3]oxazino[2,3‐b]quinazolin‐6‐one [1]

Abstract 2,3‐Dihydro‐5H‐oxazolo[2,3‐b]quinazolin‐5‐one 5a was synthesized from anthranilamide 1 and 2‐chloro‐ethyl isocyanate either by a direct reflux in methanol, or by stirring at room temperature in acetonitrile leading to the intermediate, 2‐(2‐chloroethyl ureido)benzamide 6a which was subsequently cyclized on heating with an organic base. However, when compound 6a was refluxed with concentrated hydrochloric acid, it furnished 3‐(2‐chloroethyl)‐2,4‐dioxo‐1H,3H‐quinazoline 2a in good yields. 3,4‐Dihydro‐2H,6.H‐[1,3]‐oxazino[2,3‐b]quinazolin‐6‐one 5b, 3‐(3‐chloropropyl)‐2,4‐dioxo‐1H,3.H‐quinazoline 2b and 2‐(3‐chloropropyl ureido)benzamide 6b were obtained similarly from 1 and 3‐chloropropyl isocyanate.