SYNTHESIS AND PROPERTIES OF CHALCONES BASED ON DEHYDROACETIC ACID

Abstract

The Knoevenagel condensation reaction between dehydracetic acid and aromatic aldehydes is described in this work. The reaction is carried out directly between dehydroacetic acid and aromatic aldehydes in the presence of organic bases. The optimal conditions for the Knoevenagel reaction based on dehydroacetic acid and various aldehydes were determined. Twenty-one chalcones with substituents of different nature were synthesized. The composition and structure of the obtained compounds were determined. All characteristic signals of chalcones are present in the 1H NMR spectra of the obtained compounds registered in CDCl3 and DMSO-d6: OH groups in the range of 18.7–16.5 ppm, CH proton – 6.3–5.9 ppm, and methyl group of the pyran cycle 2.3–2.2 ppm. The corresponding signals of methine protons and aryl substituents are also present in the spectra. The most sensitive to solvent changes is the OH proton bound by an intramolecular hydrogen bond to the carbonyl group of the pyran ring. Signals in DMSO are usually shifted by 0.1–1.0 ppm in a stronger field compared to CDCl3 for dehydroacetic acid and chalcones based on it. CH proton signals are shifted by approximately 0.3 ppm in a weaker field, and the signals of the protons of the methyl group are almost insensitive to the solvent. The optical properties of obtained compounds were investigated in DMF, MeOH, MeCN. The synthesized chalcones absorb light in the visible range 330–490 nm with molar extinction coefficients of 3.5–4.5. The solvatochromic effects for most of them are weak – the position of the maximum changes by less than 10 nm. The electron-donor substituents in the phenyl ring (-NMe2 and -NEt2) shift the absorption ma­ximum bathochromically by almost 100 nm compared to others in all investigated solvents.