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, N -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.