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■ Synthesis and Reactivity of 2-Chloro-3-formylpyrido[2,1-a]isoquinoline Derivative. A Novel Routes to Pyrazolo[3',4':4,5]pyrido[2,1-a]isoquinoline and Isoquinolino[2,1-g][1,6]naphthyridines

Hamdi M. Hassaneen,* Wagnat W. Wardkhan, and Yasmin Sh. Mohammed

*Department of Chemistry, Faculty of Science, Cairo University, Giza 12613, Egypt

Abstract

Treatment of 2-hydroxy-9,10-dimethoxy-4-oxo-6,7-dihydro-4H-pyrido[2,1-a]isoquinoline-1-carbonitrile 2 with POCl3/DMF gave 2-chloro-3-formylpyrido[2,1-a]isoquinoline derivative 3. Compound 3 reacted with hydrazines 5a-d to give the condensation products 6a-d. Cyclization of 6a gave pyrazolo[3',4':4,5]pyrido[2,1-a]isoquinoline derivative 7. Treatment of 3 with ethoxycarbonylmethylenetriphenylphosphorane 10 afforded (E)-ethyl 3-(2-chloro-1-cyano-9,10-dimethoxy-4-oxo-6,7-dihydro-4H-pyrido[2,1-a]isoquinolin-3-yl)acrylate 11. Azidation of 11 yielded the corresponding azido compound 12. Reduction of 12 gave the corresponding amino compound 13 which upon cyclization gave the novel tetracyclic product 14. Compound 12 reacted with triphenylphosphine to give phosphorane compound 15, which reacted with phenyl isothiocyanate to give a novel isoquinolino[2,1-g][1,6]naphthyridine derivative 18. Refluxing of 11 with amines 19a-c and thiophenols 22a-d in ethanol produced the corresponding substitution products 20a-c and 23a-d, respectively. Cyclization of 20a afforded isoquinolino[2,1-g][1,6]naphthyridine derivative 21.