Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin: Experimental and computational evidence for intramolecular and intermolecular C-F⋯H-C bonds

Abstract

4-(2-Fluorophenyl)-7-methoxycoumarin (6) was synthesized by Pechmann reaction under mild conditions via a three-step reaction. The solution-state 1H NMR spectra of 6 showed a strong intramolecular interaction between F and H5 (JFH = 2.6 Hz) and 13C NMR suggested that this C-F⋯H-C coupling is a through-space interaction. The 2D 19F-{1H} HOESY and 1H-{19F} 1D experiments were done to confirm this F⋯H interaction. The single crystal X-ray structure and the DFT-optimized structure showed that the fluorinated phenyl ring favors the orientation with the fluorine atom closer to H5 than H3. The X-ray structure also showed the existence of the intermolecular C-F⋯H-C interaction.