Naphthyridines. Part III. Tetrahydro- and decahydro-1,5-, -1,6-, -1,7-, and -1,8-naphthyridines
Decahydro-1,5-, -1,6-, -1,7-, and -1,8-naphthyridines have been prepared by reduction of the respective naphthyridines with sodium and ethanol. Reduction of 1,5-naphthyridine with platinum oxide in acid solution gave a separable mixture of trans- and cis-decahydro-1,5-naphthyridine. It was possible to distinguish between these isomers, also those of trans- and cis-decahydroquinolines and decahydroisoquinolines, by proton magnetic resonance spectroscopy. Catalytic reduction of 1,5-, 1,6-, and 1,8-naphthyridine with palladium on charcoal in ethanol gave the corresponding 1,2,3,4-tetrahydro-derivatives, but 1,7-naphthyridine gave a separable mixture 1,2,3,4-tetrahydro-(57%) and 5,6,7,8-tetrahydro-1,7-naphthyridine (43%). The structures of the tetrahydronaphthyridines were established by ionisation measurements and by ultraviolet and proton magnetic resonance spectroscopy.