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Paper | Regular issue | Vol 102, No. 11, 2021, pp.2138-2152
Published online, 3rd September, 2021
DOI: 10.3987/COM-21-14530
Synthetic Approaches for Construction of Novel 3-Heteroarylchromeno[2,3-b]pyridines and Annulated Chromenopyridopyrazolopyrimidines

Magdy A. Ibrahim* and Youssef A. Alnamer

*Department of Chemistry, Faculty of Education, Ain Shams University, Roxy 11757, Cairo, Egypt


Hydrazinolysis of ethyl 2,5-dioxo-1,5-dihydro-2H-chromeno[2,3-b]- pyridine-3-carboxylate (2) afforded chromeno[2,3-b]pyridine-3-carbohydrazide 3 which utilized as a precursor for building a diversity of heterocyclic compounds at position 3. Condensation of carbohydrazide 3 with 3-formylchromone produced the condensation product 4, while addition of carbohydrazide 3 to phenyl isothiocyanate gave hydrazinecarbothioamide derivative 5 which upon cyclization afforded 3-thiadiazolylchromeno[2,3-b]pyridine-2,5(1H)-dione 6. Condensation of carbohydrazide 3 with some monoelectrophilic reagents namely ethyl chloroformate, carbon disulfide, acetyl chloride and benzoyl chloride and chromone-3-carboxylic acid gave a variety of novel 3-oxadiazolylchromeno-[2,3-b]pyridines 7-10 and 12. Treatment of carbohydrazide 3 with a variety of 1,3-bielectrophiles such as acetylacetone, ethyl acetoacetate and diethyl malonate yielded 3-(pyrazolyl)carbonylchromeno[2,3-b]pyridines 13-15. Finally, reaction of carbohydrazide 3 with ethyl cyanoacetate and (ethoxymethylene)malononitrile afforded heteroannulated chromeno[2``,3``:6`,5`]pyrido[2`,3`-d]pyrazolo[1,5-a]-pyrimidines 17 and 18. Structures of the synthesized products were confirmed based on their analytical and spectral data.