MNDO3-Nitropyridine and some of its derivatives are aminated in a liquid ammonia solution of potassium permanganate to the corresponding 2-and (or) 4-and (or) 6-amino compounds.Quantumchemical calculations for a few 3-nitropyridines suggest that the experimentally observed regioselectivity of the amination is controlled by Coulombic interaction.Nucleophilic displacement of hydrogen in nitropyridfnes by the amino group occurs only with difficulty. Usually, under the classical conditions of the Chichibabin amination (amide ion in an inert solvent or in liquid ammonia) decomposition of the substrate takes place, and consequently the yield of the amino product is very low, if any','). Recently, we have reported on the successful amination of some nitroazanaphthalenes by means of the liquid ammonia/potassium permanganate system 3--5). As intermediates in these amination reactions amino-o-adducts (e. g. 2) are formed which are subsequently oxidized to the amines6), e.g. 1 + 2 + 3 (Scheme 1).
Scheme 1If the electron deficiency of the aromatic ring is sufficiently high the amino-o-adducts are formed rapidly in appreciable concentration and can be detected by NMR technique6'. The mentioned reactions of oxidizing aminodehydrogenation proceed under mild conditions and allow the facile preparation of a number of aminonitroazanaphthalenes.To explore the further potential synthetic use of the amination reactions we have studied the behavior of some mononitropyridines toward liquid ammonia/potassium permanganate. The results obtained are given below (Scheme 2).
Results and DiscussionThe structure of the obtained amino compounds has been established on the basis of spectroscopic data, especially 'H-NMR spectral data7), or by a comparison of their properties with those of reference compounds.2-and 4-nitropyridine do not react with liquid NHJ KMn04 at -33°C for 5 h, and starting material is recovered quantitatively. In contrast, 3-nitropyridine (4a) is converted into a mixture of 2-, 4-, and 6-amino-3-nitropyridines (5a, 5b, and 5c). Moreover, in the reaction mixture, besides unreacted starting material, a small amount of 2,6-diamino-3-nitropyridine (5d) has been found. The ratio of amino compounds formed from 4a reflects the susceptibility of three electron-deficient positions in 3-nitropyridine for the ammonia attack'). The ratio of 5a:5b:5c is measured by Scheme 2 R1 R1
3-, 5-, 6-, 7- and 8-Nitroquinolines react with 4-amino-1,2,4-triazole in basic medium (potassium tert-butoxide-dimethyl sulfoxide) giving amino products of the vicarious nucleophilic substitution (VNS) of hydrogen, predominantly at ortho position to the nitro group, except 8-nitroquinoline, which reacts at para position. Additionally, furazano[3,4-f]- and furazano[3,4-h]quinoline were obtained in the case of 5- and 8- nitroquinoline, respectively. 2-Nitroquinoline was aminated to 2-quinolino(1,2,4-triazol-4-yl)amine in these conditions.Key words: nitroquinolines, vicarious nucleophilic substitution (VNS), 4-amino-1,2,4-triazole.
1,3-Dinitrobenzene (la) and some simple monosubstituted derivatives (lb-g) were aminated with a liquid methylamine solution of potassium permanganate (LMA/PP) to give the corresponding mono-and bis(methy1amino)-substituted compounds (3a-e and 4a). 1,2-Dinitrobenzene ( l i ) was aminated with LMA/PP to give 2-(rnethylamino)-l-nitrobenzene (3f) in high yield. The intermediacy of 4-(methylamino) a-adducts of 1,3-dinitrobenzene (2a), 2-chloro-(2b) and 2-amino-1,3-dinitrobenzene (2c) was established by ' H-NMR spectroscopy. Quantum-chemical calculations for the dinitrobenzenes suggest that, in general, the experimentally observed regioselectivity of the methylamination is satisfactorily described by frontier molecular orbital (FMO) interaction of the reagents.
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