Synthesis and characterization of new chromeno[2,3-b]pyridines via the Friedl nder reactions of 8-allyl-2-amino-4-oxo-4H-chromene-3-carboxaldehyde

New series of chromeno[2,3-b]pyridines, 2-8, have been obtained from 1,8-diazabicyclo [5.4.0]undec-7-ene catalyzed Friedl nder reaction of 8-allyl-2-aminochromone-3-carboxaldehyde (1) with some carbonyl compounds containing a reactive α-methyl or methylene group namely 2-acetylthiophene, 3-acetylpyridine, 4-chloroacetophenone, 4,6-diacetylresorcinol, acetylacetone, dibenzoyl methane and acetoacetanilide. Heteroannulated chromones, 13-16, were prepared from Friedl nder reaction of 1 with some cyclic α-methylene ketones namely 2-phenyliminothiazolidin-4-one, pyrazoline-3,5-dione, 5,5-dimethylcyclohexane-1,3-dione and thiobarbituric acid. Structures of the newly synthesized compounds have been established from elemental analysis and spectroscopic data.