No abstract
547.814.5 V. V. Ishchenko, and V. P. Khilya 3-(2-Pyridyl)coumarins were prepared by reaction of substituted salicylaldehydes and 2-pyridylacetonitrile. Benzylation, acylation,coumarin was studied.Compounds with a coumarin ring are widely distributed throughout the plant kingdom and much less in animals. They belong to a large group of so-called phenolic compounds, the formation of which is characteristic of all representatives of the plant kingdom. Therefore, the important role in the life-cycle of plants of these compounds, which contribute to plant protective reactions and in many instances their pigmentation, cannot be disputed.As a rule, coumarins in nature occur as glycosides (highest contents in plants of the Umbelliferae, Rutaceae, Solanaceae, and Fabaceae families). Natural coumarins have been used in medicine (anticoagulants), foods, and fragrances. Synthetic coumarins and their analogs are used as fluorescent probes and markers for biological research and as antibiotics, antiallergens, and fungicides in medicine.We studied the synthesis of coumarins with a pyridine substituent via Knoevenagel condensation of substituted salicylaldehydes with 2-pyridylacetonitrile [1-8]. The resulting 2-iminocoumarins were converted to coumarins 1-10 by hydrolysis of the imine (Scheme 1). Scheme 1.Properties of the synthesized compounds (1-10) and their IR, UV and PMR spectra are given in the Experimental section.The most characteristic signal in the PMR spectra of the 3-(2-pyridyl)coumarins is that for the coumarin 4-H, a singlet at 8.70-8.95 ppm. The signals of the other coumarin protons depend on the nature and position of the substituent in the coumarin ring whereas the signals for the pyridine protons are practically the same in all compounds 1-10: (3′-H: 8.2-8.5 ppm, br.d, 3 J = 8 Hz; 4′-H: 7.8-7.9 ppm, br.t, 3 J = 8 Hz; 5′-H: 7.2-7.4 ppm, br.t, 3 J = 4.5-6 Hz; 6′-H: 8.7-8.9 ppm, br.d, 3 J = 4.5-6 Hz).Two planar conformations (I and II) are possible for 3-(2-pyridyl)coumarins. In these, the pyridine and coumarin systems are conjugated:
CN Het + N H O Het NH R 1 H + O Het O 1 -121 -6: Het = 2-quinolyl; 1: R 1 = H; 2: R 1 = 7-OH; 3: R 1 = 6-NO 2 ; 4: R 1 = 6-Cl; 5: R 1 = 6,8-Cl 2 ; 6: R 1 = 6-Br; 7 -12: Het = 2-(5-carbethoxyfuryl); 7: R 1 = 7-OH, 8: R 1 = 8-OH; 9: R 1 = 7,8-(OH) 2 ; 10: R 1 = 6-NO 2 ; 11: R 1 = 6-Cl; 12: R 1 = 6-Br R 1 547.814.5 V. V. Ishchenko, and V. P. Khilya 3-(2-Quinolyl)-and 3-(5-carbethoxyfuryl-2)coumarins were prepared by reaction of substituted salicylaldehydes and hetarylacetonitriles. Alkylation and acylation of 3-hetaryl-7-hydroxycoumarins were studied.The variety of synthetic 3-hetarylcoumarins includes few with furan [1, 2] and quinoline [3] rings. The furan ring is found in many substances of natural origin, as a rule, in the hydrogenated form (furanose form of carbohydrates, alkaloid pilocarpine) and in synthetic biologically active compounds (furacilin antibiotics). Natural derivatives of quinoline, namely the alkaloids of cinchona tree bark quinine and cinchonine, were first used as antimalarials. Therefore, it was interesting to prepare and study coumarins with furan and quinoline as the heterocyclic substituent. Coumarins 1-12 were synthesized by condensation of substituted salicylaldehydes and hetarylacetonitriles with subsequent hydrolysis of the resulting 2-iminocoumarins in acidic medium (Scheme 1) [4]:
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