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.
Highlights
Coumarins constitute one of the big classes of naturally occurring compounds
4-(2-Fluorophenyl)-7-methoxycoumarin (6) was synthesized under mild conditions via a three-step reaction (Scheme 1) and the first step was the synthesis of the fluorinated β-keto ester 3
The last step of the synthesis was the methylation of the hydroxy group of coumarin 5
Summary
Coumarins constitute one of the big classes of naturally occurring compounds. Coumarins have been reported to play a vital role as food and cosmetics constituents, cigarette additives, and dye-sensitized solar cells [3,4]. The variety of uses of these compounds resulted in an increase in demand for large quantities of coumarins. Due to an insufficient natural supply to meet this demand for these compounds, numerous methods for the synthesis of these compounds have been developed, examples are the Pechmann condensation [10,11], Stille coupling reaction [12], Knoevenagel condensation [13], Heck coupling reaction [14], Kostanecki reaction, Baylis–Hillman reaction [15], Michael reaction [16], Suzuki–Miyaura cross-coupling reaction [17], Negishi cross-coupling reaction [18] and Wittig reaction [17].
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