Synthesis, structural and conformational study of chromane derivatives

2-Methyl-4-oxo-4H-chromene-3-carboxylic acid methyl ester (1) and 2-phenyl-4-oxo-4H-chromene-3-carboxylic acid ethyl ester (2) were reacted with NaBH4 to give 2-R-2,3-dihydro-4-hydroxy-2H-1-benzopyran-3-carboxylic acid esters (3: methyl ester, R = methyl, 4: ethyl ester, R = phenyl – respectively). The structures of resultant compounds 3 and 4 were confirmed by IR, 1H NMR spectroscopy, mass spectrometry and elemental analysis. Additionally the X-ray analysis of the compound 3 revealed that hydrogen atoms bonded to the C2 and C4 atoms are in axial positions and hydrogen atom bonded to C3 atom is in equatorial position. The main conformation in solution for both compounds is similar and was confirmed based on the 3JHH coupling constants obtained from experimental spectra and from DFT conformational analysis.