Preparation of New Nitrogen-Bridged Heterocycles. 18. Facile Formations of 3-Arylpyrazolopyridines and 1-Arylindolizines

Article abstract of DOI:10.1246/bcsj.61.2055

The alkaline teratment of 1-<(substituted benzylthio)methyleneamino>pyridinium and 1-<2-(substituted benzylthio)vinyl>pyridinium bromides possessing an electron-withdrawing substituent such as a nitro or cyano group in the presence or absence of a dehydrogenating agent afforded the corresponding 3-arylpyrazolo<1,5-a>pyridines and 1-arylindolizines in moderate to good yields, while the reactions of the parent pyridinium salts and those having an electron-releasing group did not produce any significant products.The mode of the reaction, a ring contraction-desulfurization, is the same as that observed in related monocyclic species.