2006Benzopyran derivatives R 0350 3-(4-Phenyl-1,2,4-triazol-3-yl)chromones. -Based on acetophenones of type (III), a series of isoflavones is prepared. Compound (IIIc) is obtained in very low yield due to tarring of the product. -(SHOKOL, T. V.; TUROV, V. A.; TUROV, A. V.; KRIVOKHIZHA, N. V.; SEMENYUCHENKO, V. V.; KHILYA, V. P.; Chem.
It is known that 3-aryl-4-triazolylpyrazoles show fungicidal, herbicidal, and growth regulator activity [1,2]. 5-Aryl-4-triazolylisoxazoles have been patented as insecticides and acaricides [3]. It was of interest to prepare similar, potentially biologically active compounds based on one starting product. With this in mind we decided to use a route based on the recyclization of chromones using the binucleophiles hydrazine, hydroxylamine, and amidines [4,5]. It is known the chromone ring undergoes fission with nucleophiles to form a substituted acetophenone and the presence of a second nucleophilic center leads to an attack at the carbonyl carbon atom with closure of the corresponding five-or six-membered ring.The 2,6,8-substituted 7-hydroxy-3-(4-phenyl-1,2,4-triazol-3-yl)chromones 1a,f [6,7] were selected as starting materials. It has previously been found that reaction of 2-substituted chromones with hydroxylamine forms isoxazoles while the recyclization of chromones unsubstituted in the 2 position can proceed further with a subsequent recyclization of the isoxazole ring to 2-aminochromone. Moreover, the ratio of isoxazole to 2-aminochromone depends on the heterocycle in position 3 of the chromone [8].Refluxing 2-carbethoxy-3-(4-phenyl-1,2,4-triazol-3-yl)chromones 1d,e in pyridine with an excess of hydroxylamine hydrochloride gave the isoxazoles 2d,e. The 1 H NMR spectra of these compounds show the absence of a low field singlet near 11 ppm typical of the 7-OH group in the starting chromones 1d,e. At the same time there are observed two singlets at higher field 8.9-9.7 ppm which are assigned to the 4-and 2-OH groups of a phenol ring. The aromatic proton signals are also shifted to higher field by 0.5 ppm when compared with the protons signals in the chromone ring.Introduction into the reaction with hydroxylamine of 2-unsubstituted chromones 1b,c under the same conditions gave the 2-aminochromones 3b,c, the majority of whose 1 H NMR signals occurred in the same regions as the starting chromones 1b,c. A difference is observed only in that, in place of the singlet at 8.6 ppm for the H-2 proton, in the products 1b,c there appears a broadened, two-proton 2-amino group singlet which exchanges with D 2 O and actually appears in the aromatic proton absorption region (7.45-7.48 ppm). In contrast to the isoxazoles 2 the 2-aminochromones 3b,c are high melting compounds, poorly soluble in the majority of organic solvents. __________________________________________________________________________________________ TarasShevchenko
The condensation of 4-phenyl-1,2,4-triazol-3-ylacetonitrile with 2-methyl-, 4-ethylresorcinol, and with pyrogallol gave α-(4-phenyl-1,2,4-triazol-3-yl)-2,4-dihydroxyacetophenones. Upon treatment with acid anhydrides and chlorides and subsequent hydrolysis these form 7-hydroxy-3-(4-phenyl)-1,2,4-triazol-3-yl)chromones with different substituents in both the benzene and the pyrone rings.Keywords: 8-R 1 -6-R 2 -2-R 3 -7-hydroxy-3-(4-phenyl-1,2,4-triazol-3-yl)chromones, α-(4-phenyl-1,2,4-triazol-3-yl)-3-R 1 -5-R 2 -2,4-dihydroxyacetophenones.3-Hetarylchromones are now a rather broad class of compounds having different biological activity [1][2][3]. However, only isolated examples of triazole analogs of isoflavones are known (3-(4H-1,2,4-triazol-3-yl)- [4,5], 3-(2H-1,2,3-triazol-4-yl)chromones [6], and 2,3-dihydro-3-(1H-1,2,4-triazol-1-yl)chromones [7]), with the latter patented as fungicides. The starting materials for their synthesis are the corresponding α-triazolyl-2-hydroxyacetophenones. 3-(4,5-Dihydro-1H-1,2,4-triazol-5-yl)chromones have been isolated amongst the products of the 1,3-dipolar cycloaddition of 3-(aryliminomethyl)chromones and C-acetylhydrazinoyl bromides [8].With the aim of broadening the scope of triazole analogs of isoflavones we have synthesized a series of starting α-(4-phenyl-1,2,4-triazol-3-yl)-2,4-dihydroxyacetophenones (1a-c) with different substituents in the phenyl ring via condensation of 4-phenyl-1,2,4-triazol-3-ylacetonitrile with 2-methyl-and 4-ethylresorcinol and with pyrogallol. Modified Hoesch reaction conditions were used with boron trifluoride etherate as solvent and catalyst.It should be noted that the products 1a,b are obtained in chromatographically pure form and in high yields (78-80%) (as was found in the case of the condensation with the resorcinol (1d)) but the pyrogallol derivative 1c was obtained in only 22% yield, very likely due to tarring of the reaction product.Compounds 1 can exist in the ketone (A) and enolic (B) forms. Rapid recrystallization of compound 1b from ethanol gave a 50% yield of a colorless product, the 1 H NMR spectrum of which (DMSO-d 6 solvent) showed the presence of a two-proton methylene singlet at 4.53 ppm and two low field singlets at 10.49 and 11.68 ppm which are assigned to the hydroxyl groups in the positions 4 and 2 of phenolic ring respectively. Thus the sample exists in the ketone form A only. After two weeks a light-yellow product is precipitated from the mother liquor whose 1 H NMR spectrum (DMSO-d 6 ) shows both the signal for the methylene group of ketone A at 4.53 ppm and also signals for a methine proton at 5.29 ppm and enolic proton at 14.09 ppm for the enol form (B) together with a double set of the remaining signals. Thus, in this case, we have shown the presence of ketoenol tautomerism with an isomer ratio of 84% (A) to 16% (B) as judged by the integrated intensities of the signals. With a more prolonged crystallization process the enol content of the sample is ___________________________________________________________________...
Cyclohexyldihydroxanthyletin derivatives with S and N in place of the exocyclic O atom were synthesized. The structures of the products were proved by NMR correlation spectroscopy.
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