Keywords: 1-amino-4-methylpyridine, α-chlorooxirane, α-hydroxy acid, imidazo[1,2-a]pyridine, heterocyclic carbaldehyde.The presence in α-chloroepoxides of type 1 of a potential aldehyde group -the acetal fragmentpredetermines the high reactivity of these electrophilic reagents. We have shown that acetal-containing α-chlorooxiranes [1] are suitable starting reagents for the synthesis of five-and six-membered heterocyclic carbaldehydes and their derivatives [2][3][4].To widen the synthetic potential of these substrates and to obtain polyheterocycles we have studied the condensation of α-chlorooxirane 1 with the aminopyridine 2. The reaction occurred in boiling isopropanol over 3 h to give the heterocycle 9.The very unexpected formation of compound 9, the structure of which was proved by 1 H NMR and X-ray crystallography, may occur as shown in the scheme (r.p. 1900).Heterocyclization occurs in the first step to form the acetal 3 which is easily converted into the carbaldehyde 4 in the acid medium. An unusual condensation of the polyaminal 5, formed by reaction of the aldehyde 4 with a second molecule of aminopyridine 2, with the product of the rearrangement of α-chlorooxirane -the α-chloro ketone 6 -then occurs, accompanied by the formation of a new carbon-carbon bond. In previous investigations we have shown that heterosubstituted α-chloroacetals in acid media underwent redox processes which led to the synthesis of α-hydroxy acids [5]. Evidently the intermediate α-keto acetal 7 was converted similarly to the hydroxy acid 8. The latter was transformed into the final product 9 by intramolecular condensation.
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New functionalized condensed benzazoles have been synthesized based on isatin, 3,4-diaminofurazane, and sodium diformylimide.Many dyes, plant growth stimulators, analytical reagents, and medical preparations have been obtained based on isatin [1][2][3]. The furazane ring is found in energy-rich materials, intermediates in organic synthesis, and biologically active compounds [4,5].With the objective of finding new biologically active compounds based on isatin 1 and 3,4-diaminofurazane 2 as nucleophilic reagent we have synthesized heterocycles containing indole and furazane rings at the same time. The interaction of compounds 1 and 2 was carried out by boiling in acetonitrile. The reaction did not occur at room temperature which is probably connected with the low nucleophilicity of the amino groups in 3,4-diaminofurazane.The course of the reaction was monitored by the disappearance in the IR spectrum of the C=O vibration in position 3 of isatin and by TLC. The reaction mixture became darker during the course of the reaction. Analytically pure compound 3 was obtained by column chromatography with subsequent recrystallization from absolute ethanol. The spiro compound 3 was isolated in 77% yield.
The reaction of phosphorylated α-chloroacetaldehydes with 3,4-diaminofurazane gives enamines, bisenamines, semiaminals, and O,N-acetals, whose cyclization leads to previously unreported phosphorylated furazano[3,4-b]piperazines.Derivatives of furazano [3,4-b]piperazines are used as energy-rich materials, intermediates in organic synthesis, and biologically active compounds. However, preparative methods for obtaining these compounds and the chemical properties of these derivatives, which may have potential as biologically active compounds, have not been studied adequately [1,2].With the aim of synthesizing C-phosphorylated furazanopiperazines, we studied the reactions of α-chloroacetaldehydes 1 with diaminofurazane. The condensation of phosphorylmonochloroacetaldehydes 1a,b with 3,4-diaminofurazane proceeds in ethanol at reflux and leads to the formation of monoenamine 2 and bisenamine 3 depending on the ratio of the starting reagents. + 2, 3 a R = Et, b R = i-Pr Enamines 2 and 3 are white crystalline compounds. The IR band for their amino group is found at 3350 cm -1 and is superimposed on the stretching band of the secondary amino group to give a complex overall shape. The low value for ν NH 2 in KBr pellets indicates hydrogen bonding of this group.
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