Application of Nickel Complexes with 1,3-Dicarbonyl Compounds for Synthesis of Fused 4-Aminopyridine-Based Systems
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ication of Nickel Complexes with 1,3-Dicarbonyl Compounds for Synthesis of Fused 4-Aminopyridine-Based Systems R. N. Vydzhaka, S. Ya. Panchishina, and V. S. Brovaretsa,* a
V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine, Kiev, 02094 Ukraine *e-mail: [email protected] Received March 27, 2020; revised March 27, 2020; accepted April 10, 2020
Abstract—A potential of using nickel complexes with 1,3-dicarbonyl compounds for the transformation of heterocyclic aminonitriles into fused systems with a 4-aminopyridine core was evaluated. A possibility of introducing acidophobic groups into the molecules of fused compounds was shown. Keywords: nickel complexes with 1,3-dicarbonyl compounds, oxadiazolo[3,4-b]pyridines, triazolo[4,5-b]pyridines, pyrazolo[3,4-b]pyridines
DOI: 10.1134/S1070363220080101 Over the past decades, much attention has been given to the development and improvement of synthetic approaches to the preparation of azoloazines. Among such fused nitrogen-containing heterocycles, an important place belongs to 4-aminopyridine derivatives, which are promising scaffolds for the search for biologically active compounds. The literature data include the following approaches to the synthesis of such compounds: – reduction of nitro derivatives of azolopyridines, however, this method is practically not used due to the low availability of nitro derivatives [1–4]; – substitution of a halogen atom or alkoxyl group for an amino group; the main disadvantage of this approach is low availability of the corresponding halo- and alkoxyazolopyridines [5–7]; – substitution of the halogen atom with the azido group followed by reduction to the amino group [8, 9]; – annulation of the azole fragment to the substituted 4-aminopyridine; this method is not often used, since it requires the preparation of specifically substituted 4-aminopyridines [10–12]; – raction of heterocyclic aminonitriles with carbonyl compounds in the presence of Lewis acids (ZnCl2, AlCl3, SnCl4) is more often than others used to obtain azolopyridines [13–19], however, the yield of final products, as a rule, does not exceed 50%; significant
restrictions are imposed on the presence functional groups in the molecules of the starting reagents; – addition of carbonyl compounds to the nitrile group of cyanoazoles in the presence of bases with further transformation of intermediate products into azolopyridine derivatives [20–24]. Alkali metal alcoholates, potassium carbonate, amines or complexes of 1,3-dicarbonyl compounds with transition metals are used as bases. On the other hand, nickel acetylacetonate has been known to add cyanogen [25] and other electrophilic heterocyclic nitriles under mild conditions [24]. It is also an effective catalyst for the preparation of Michael adducts of acetylacetone with unsaturated compounds. The yields of the final products are always significantly higher than in traditional syntheses using strong bases [26]. The aim of this work is to evaluate the possibility of using nicke
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