Nitrogen Bridgehead Compounds. Part 79. Synthesis and structure elucidation of benzimidazolo[2,1-f][1,6]naphthyridine aza-derivatives

6-Substituted 1,6-naphthyridine-5(6H)-ones were prepared from diethyl 2-2-(dimethylamino)vinyl]-6-methylpyridine-3,5-dicarboxylate 1 2] by ring closure with aromatic and heteroaromatic diamines (o-phenylenediamine, 2,3-diaminopyridine, 3,4-diaminopyridine and 4,5-diaminopyrimidine, respectively). 1,6-Naphthyridine-5(6H)-ones were cyclised in phosphoryl chloride to yield nitrogen bridgehead tetracycles 6-9 . The structure of the products was established by nOe difference spectroscopy. A complete ¹H and ¹³C nmr assignment was achieved by different 2D carbon-proton correlation measurements.