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5-Phenyl(p-tolyl)isoxazole-3-carboxylic acids were synthesized starting from 3-hydroxyiminomethyl-5-phenyl(p-tolyl)isoxazoles, and their reactions with p-hydroxybenzaldehyde, vanillin, isovanillin, o-vanillin, and ethyl vanillin gave the corresponding esters. The latter were brought into condensation with aromatic amines to obtain Schiff bases which were reduced to amines.Isoxazole heteroring is a structural fragment of molecules of many compounds possessing biological activity [1]. Vanillin and some substituted benzaldehydes also exhibit biological activity; in particular, they inhibit DNA-protein kinase and control DNA double strand break repair following NHEJ path (nonhomologous DNA end-joining) [2].The goal of the present study was to synthesize compounds containing substituted benzaldehyde and isoxazole residues in a single molecule, which could be promising for biological assays. Isoxazole fragment was introduced into molecules of p-hydroxybenzaldehyde, vanillin, isovanillin, o-vanillin, and ethyl vanillin with the use of 5-phenyl-and 5-(p-tolyl)isoxazole-3-carbonyl chlorides VII and VIII which were synthesized from the corresponding accessible 3-hydroxyiminomethyl-5-phenyl(p-tolyl)isoxazoles III and IV according to the procedure described by us previously [3]. 5-Arylisoxazole-3-carbaldehyde oximes III and IV were converted into carbonitriles V and VI by the action of acetic anhydride in pyridine. Hydrolysis of V and VI in aqueous-alcoholic potassium hydroxide gave carboxylic acids I and II, and the latter were treated with thionyl chloride to obtain target acid chlorides VII and VIII (Scheme 1). The yields of isoxazolecarbonitriles V and VI were 91-98%, and acids I and II were isolated in 78-88% yield. The yield of nitriles V and VI strongly depended on the presence of water in the reaction mixture, which led to the formation of the corresponding carboxamides as byproducts.The structure of compounds I, II, V, and VI was determined on the basis of their elemental compositions and IR, 1 H and 13 C NMR, and mass spectra. The IR spectra of nitriles V and VI contained absorption bands at 2254-2257 cm -1 due to stretching vibrations of the C≡N bond, and carboxylic acids I and II displayed carbonyl stretching vibration band at 1707 cm -1 . The C≡N carbon atom resonated in the 13 C NMR spectra of V and VI at δ C 110 ppm; no such signal was present in the spectra of acids I and II, but a signal typical of carboxy group appeared at δ C 171 ppm. The mass spectra of compounds I, II, V, and VI contained the molecular ion peaks and peaks from fragment ions.By reaction of carboxylic acid chlorides VII and VIII with p-hydroxybenzaldehyde, vanillin, isovanillin, o-vanillin, and ethyl vanillin in diethyl ether in the presence of an equimolar amount of triethylamine we obtained 84-93% of the corresponding esters IX-XVIII. Esters IX-XVIII showed in the IR spectra absorption bands belonging to stretching vibrations of the ester and aldehyde carbonyl groups at 1748-1765 and 1679-1702 cm -1 , respectively. In the 1 H NMR spectra...