This literature about this compound(1569-17-1)Synthetic Route of C9H8N2has given us a lot of inspiration, and I hope that the research on this compound(4-Methyl-1,8-naphthyridine) can be further advanced. Maybe we can get more compounds in a similar way.
In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called Synthesis of 1,8-naphthyridine homologs and their hydrogenation, published in 1941, which mentions a compound: 1569-17-1, Name is 4-Methyl-1,8-naphthyridine, Molecular C9H8N2, Synthetic Route of C9H8N2.
In earlier work (CA 33:2525.5) it was found that Me 1,4-dihydroxy-2,5-naphthyridine-3-carboxylate (C. A. numbering, 5,8-dihydroxy-1,6-naphthyridine-7-carboxylate) and the 1-Cl compound on catalytic hydrogenation take up H only on the nonsubstituted pyridine ring. In continuation of this work, 2,4-dimethyl- (I) and 4-methyl-1,8-naphthyridine (II) have been synthesized and a similar phenomenon on hydrogenation has been observed. In the meantime some other 1,8-naphthyridines described in this paper have been prepared by analogous methods by Mangini (preceding abstract). 7-Amino derivative of I (0.5 g. from 2 g. 2,6-diaminopyridine, 2 g. CH2Ac2 and 1 g. fused ZnCl2 heated 3 hrs. at 120-30°), m. 220° (Ac derivative, pale yellow, m. 300°), converted by diazotization in 40% H2SO4 into the 7-HO compound, m. 251°, which, heated 30 min. in a sealed tube at 140° with POCl3, gives the 7-Cl compound, m. 146-7°; this, boiled 30 min. with 20% MeONa in MeOH, gives the 7-MeO compound, m. 65° (picrate, m. 188-9°). Hydrogenation of 1 g. of the HO compound in 20 g. alc. with 1 g. Ni-kieselguhr under 110 atm. of H for 10 hrs. at 170-80° gave, along with 0.6 g. unchanged material, 0.2 g. of a dihydro derivative, C10H12N2O, m. 175-80°. The Cl compound (0.5 g.), shaken in 10% KOH-MeOH with 0.2 g. of 20% Pd-charcoal and H until about 1.2 mols. H had been absorbed, and the product chromatographed in benzene through Al2O3, yielded about 0.05 g. I, m. 85-6° (HCl salt, decomposes 240°; picrate, decomposes 204-6°; methiodide, yellow needles with 1 H2O, m. 93-4; chloroplatinate, I.H2PtCl6, decomposes 242-4°; chloroaurate, decomposes 166-7°). When 0.1 g. of the Cl compound in 10 cc. of 10% KOH-MeOH was hydrogenated to saturation with 0.5 g. of 20% Pd-charcoal it yielded the tetrahydro derivative (III) of I described below. With 1.2 g. of the Cl compound in 20 cc. of 5% KOH-MeOH, 0.5 g. PdO-CaCO3 and a trace of Pd-charcoal, the hydrogenation stopped in 30 min. (about 170 cc. H absorbed) and 0.8 g. I was obtained. Shaken in 10 cc. AcOH with 0.1 g. Pt oxide and H to saturation, 0.5 g. I absorbed about 160 cc. H and yielded 0.5 g. of a tetrahydro derivative (III), m. 118°, giving a pos. Liebermann reaction (picrate, m. 207°; Ac derivative, m. 42-3°); III was also obtained in 0.85-g. yield from 1 g. I in 50 cc. cyclohexane and 5 cc. alc. with 1 g. Raney Ni heated under an initial H pressure of 70 atm. 2 hrs. at 120° and 2 hrs. at 190°. III was unchanged by 4 hrs. treatment in AcOH with Pt oxide and 110 atm. H pressure, at room temperature With Na in boiling alc., however, it yielded the decahydro derivative of I, easily subliming needles, m. 92-3° (di-Ac derivative, thick oil, b0.02 135-45°). 2,7-Dichloro-4-methyl-1,8-naphthyridine in 10% KOH-MeOH hydrogenated with PdO-CaCO3 and a trace of Pd-charcoal gave, together with a mono-Cl compound, C9H7ClN2, m. 104°, chiefly (about 70%) II, b0.05 147-8° (picrate, decomposes 204-5°; perchlorate, m. 180-1°). II (1 g.) in 10 cc. AcOH with 0.5 g. Pt oxide and H yielded a mixture of 2 isomeric tetrahydro derivatives, separated by fractional crystallization from petr. ether: 0.2 g. of a more soluble isomer A (IV), m. 62-3°, giving a pos. Liebermann reaction (Bz derivative, m. 86-7°), and about 0.8 g. of a less soluble isomer B (V), m. 102-3° (picrate, decomposes 248°; Bz derivative, m. 105-6°; nitro derivative, m. 217-18° and giving a pos. Liebermann reaction, prepared by treating the tetrahydride in cold H2SO4 (dry ice-acetone) with fuming HNO3 (d.1.6), pouring on ice, crystallizing from alc., heating the crystals (m. 124-5°) in concentrated H2SO4 at 60°, again pouring on ice, filtering, making alk. with Na2HPO4 and extracting with ether). V is unchanged by hydrogenation in AcOH with PtO and 65 atm. H pressure. With Na in boiling AmOH, both isomers yield the same (racemic) decahydro derivative of II, b0.1 70-80°, m. 87°, gives a pos. Liebermann reaction (picrate, decomposes 210°). The structures of III, IV and V have not been definitely established but the following considerations make it highly probable what they are. The work of earlier investigators on the hydrogenation of quinoline homologs with Ni and H under pressure and with Sn and HCl has shown that Me groups have a disturbing influence on the hydrogenation of the ring half on which they are substituted whereas Na and alc. readily hydrogenate the Me-substituted rings. This disturbing effect of Me groups is ascribed to the inductive effect of the Me group. III is considered to be the 5,6,7,8-tetrahydro compound To further confirm this, III was heated in a little alc. with an excess of ClCH2COMe for 4 hrs. at 100°; the resulting addition product, C15H21ClN22O2, m. 181-2°, allowed to stand 1 day in a little water with 2 drops of 10% Na3CO3, gave, in addition to unchanged III, a resin whose blue Ehrlich reaction pointed to the presence of an indolizine ring. Such a ring can be formed only from a nonhydrogenated 2-methylpyridine. IV is considered to be the 1,2,3,4- and V the 5,6,7,8-tetrahydro compound because the latter is formed in the larger amount; its higher m. p. is also in harmony with such an assumption.
This literature about this compound(1569-17-1)Synthetic Route of C9H8N2has given us a lot of inspiration, and I hope that the research on this compound(4-Methyl-1,8-naphthyridine) can be further advanced. Maybe we can get more compounds in a similar way.
Reference:
1,8-Naphthyridine – Wikipedia,
1,8-Naphthyridine | C8H6N2 – PubChem