3-Aroylacrylic acids and their functionalized derivatives are convenient bielectrophilic reagents for the synthesis of six-membered heterocycles [1][2][3][4][5]. The formal [4+2], [3+3] or [2+4] cycloaddition schemes correspond to interaction of these compounds with 1,4-, 1,3-or 1,2-binucleophiles respectively. Reactions of 3-aroylacrylic acids with -aminoazoles remain the least studied, few publications being concerned with this problem [6,7]. However, a convenient method for the synthesis of the azolopyridine or azolopyrimidine systems is the reaction of chalcone type enone systems with -aminoazoles [8]. The synthetic availability of 3-aroylacrylic acids [9, 10], the high reactivity of an activated ethylene bond [11][12][13], and the possibility of functionalization of the carboxyl group point to the evident advantages of these bielectrophiles over the chalcones.In our work we have studied the cyclocondensation of the 3-aroylacrylates 1a-d with the 5-aminopyrazoles 2a,b and the 3-aroylacrylates 1d-g with 3-amino-1,2,4-triazole (3).There are literature reports of the formation of both pyrazolo[1,5-a]pyrimidines [14-17] and pyrazolo [3,4-b]pyridines [18][19][20] in the reaction of 5-aminopyrazoles with compounds having enone structural fragments. The use of 3-aroylacrylic acid derivatives in similar reactions permits the synthesis of functionalized dihydroazoloazine systems [6].Treatment of the esters 1a-d with 5-aminopyrazole 2a in ethanol gives high yields of the pyrazolo-[3,4-b]pyridines 4a-d as yellow crystals. The formation of the pyrazolopyridine bicycle is associated above all with the nucleophilic centers of the 5-aminopyrazole molecule [18,19]. The synthesis of pyrazolopyridines 4a-d involves the formation of an α-adduct at the pyrazole 2a C-4 atom.
The reactions of 3 amino 1,2,4 triazole, 5 aminotetrazole, and 2 aminobenzimidazole with 2 aryl 4 arylidene 4H oxazol 5 ones (azlactones) were studied. The electron releasing properties of the azole ring were demonstrated to influence the reaction pathway of azlactones with aminoazoles. The structures of the resulting compounds were established by 1 H and 13 C NMR spectroscopy using spin spin decoupling and the nuclear Overhauser effect.Key words: aminoazoles, 2 aryl 4 arylidene 4H oxazol 5 ones, N [2 aryl 1 (azol 5 ylcarbamoyl)vinyl]aroylamides, N (7 aryl 5 oxo 4,5,6,7 tetrahydroazolo[1,5 a]pyrimidin 6 yl)aroylamides, cyclocondensation, NMR spectroscopy.
The reaction of 2-(aminomethyl)benzimidazole (1) with chalcones 2a–2e leads to formation of 3,5-diaryl-2-benzimidazol-2-yl-4,5-dihydropyrroles 3a–3e. The trans orientation of benzimidazol-2-yl and 3-aryl substituents in 3a–3e was established by X-ray analysis of 3e.
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