Chemical Reactivity of 4,9‐Dimethoxy‐5‐oxo‐5H‐furo[3,2‐g]chromene‐6‐Carboxaldehyde Toward Some Nucleophilic Reagents

Abstract

The chemical reactivity of 4,9‐dimethoxy‐5‐oxo‐5H‐furo[3,2‐g]chromene‐6‐carboxaldehyde (6‐formylkhellin) (1) was studied toward a diversity of nitrogen nucleophilic reagents. Reaction of carboxaldehyde 1 with some primary amines and heterocyclic amines afforded the corresponding Schiff bases. Also, the reactivity of carboxaldehyde 1 was studied toward some hydrazine derivatives, namely 7‐chloro‐4‐hydrazinoquinoline, 3‐hydrazino‐5,6‐diphenyl‐1,2,4‐triazine, N4‐phenylthiosemicarbazide, and S‐benzyldithiocarbazate. 6‐Formylkhellin (1) underwent ring transformation upon treatment with hydroxylamine hydrochloride producing 5‐hydroxy‐4,9‐dimethoxy‐7‐oxo‐7H‐furo[3,2‐g]chromene‐6‐carbonitrile (22). Some pyrimidine, [1,2,4]triazolo[4,3‐a]pyrimidine, tetrazolo[1,5‐a]pyrimidine, and diazepine derivatives linked benzofuran were efficiently synthesized. Reaction of carboxaldehyde 1 with a variety of 1,4‐binucleophiles produced furochromone‐fused benzodiazepine, pyridotriazepine, benzoxazepine, and benzothiazepine derivatives. Some unsymmetrical thiocarbohydrazones were also synthesized. Structures of the new synthesized products were deduced on the basis of their analytical and spectral data.