Reaction of 2-Methyl-4-phenyl-2, 3-dihydro-1H-pyrazolo[2, 3, 4-de][1, 5]-naphthyridine 2-Oxides with Acetic Anhydrides : Polonovski Reaction versus Mesomeric Betaine Formation

Abstract

Treatment of 2-methyl-4-phenyl-2, 3-dihydro-1H-pyrazolo[2, 3, 4-de][1, 5]naphthyridine 2-oxide (10a) with acetic anhydride and triethylamine or trifluoroacetic anhydride (TFAA) in the presence of dimethyl acetylenedicarboxylate (DMAD) gave the Polonovski reaction products 11-14 as the major products. The 3, 4-diphenyl derivative 10b, when treated with acetic anhydride and triethylamine either in the presence or the absence of DMAD, gave only the O-acetylhydroxylamine 17, while treatment of the same N-oxide 10b with TFAA in the presence of DMAD at -20°C afforded the expected cycloadduct 22 as the major product.