Synthesis
(3) Preparation of 2,3-dihydro-6-hydroxychromen-4-one: 6-methoxychromen-dihydropyran-4-one (2.9 g, 0.0163 mol) was sequentially added to a mixed solution of glacial acetic acid (20 mL) and HBr (>40%, 20 mL), stirred and refluxed for 1 h. The reaction solution was then extracted with ethyl acetate. Upon completion of the reaction, the pH of the reaction solution was adjusted to 10-11 with KOH solution, and then the pH of the aqueous layer was adjusted to 2-3 with concentrated hydrochloric acid.Subsequently, the aqueous layer was extracted with ethyl acetate, and the organic layers were combined and dried with anhydrous Na2SO4. The dried organic layer was cooled and a black solid was precipitated. The solid was recrystallized with ethyl acetate to give 2.17 g of bright yellow crystals with a melting point of 142-144 °C and a yield of 81.2%.
References
[1] Bioorganic and Medicinal Chemistry Letters, 1999, vol. 9, # 18, p. 2773 - 2778
[2] Patent: US5641789, 1997, A
[3] Patent: US2008/103307, 2008, A1. Location in patent: Page/Page column 17
[4] Patent: US5322847, 1994, A
[5] Patent: EP641792, 1995, A1
