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: