Synthesis
The general procedure for the synthesis of 5,7-dihydroxy-2H-benzopyran-2-one from resorcinol and propargyl acid was as follows: a mixture of resorcinol (1.0 mmol), propargyl acid (1.1 mmol), and Yb(OTf)3 hydrate (0.1 mmol) was placed in an open reaction vessel in a microwave reaction unit and irradiated for 2 min at 200 W (80 °C) . The reaction process was monitored by thin layer chromatography (TLC) and the eluent was CH2Cl2/MeOH (99:1). Upon completion of the reaction, the crude product was diluted with ether (Et2O) and the suspension formed was filtered under vacuum to isolate the catalyst and the precipitate was washed with ether several times. The filtrate was washed twice sequentially with 5% NaHCO3 solution (10 mL), dried over anhydrous MgSO4 and evaporated to dryness under vacuum to afford the target product 5,7-dihydroxy-2H-benzopyran-2-one.
References
[1] Synlett, 1999, # 5, p. 608 - 610
[2] Tetrahedron Letters, 2016, vol. 57, # 26, p. 2939 - 2942
[3] Synthesis, 2011, # 8, p. 1283 - 1289
[4] Journal of Natural Medicines, 2017, vol. 71, # 4, p. 735 - 744
