Abstract The novel tetracyclic ring system represented by 4 and 5 has been developed by the reactions of isatoic anhydride 1a with 3-isocyanato-4-furoyl chloride 3b and by the reaction of 4H-furo [3, 4-d][1, 3] oxazine-2 (1H), 4-dione 3a with 2-isocyanatobenzoyl chloride 1b, respectively. The synthesis as well as the mechanism of the reaction are briefly discussed.
