A new spiro annellation reaction in the isoxazole series: applications and limits. Part 2. Reactivity of ethyl 4-nitro-3-phenylisoxazole-5-carboxylate with nitrogen binucleophiles
Treatment of the title compound (5) with benzamidine and 1,3-diphenylguanidine afforded in good yields the spiro nitronate (6) and a mixture of the regioisomeric salts (12) and (13), respectively; these products were easily converted into the corresponding nitro derivatives (7), (14), and (15), respectively, with hydrochloric acid. The same nitro ester (5) reacted smoothly with o-phenylenediamine and NaH to give, after acidification, the heterospiran (16). Some limits of this spiro annellation process are emphasized. The structures of the new compounds have been established on the basis of spectral data.