A Novel Synthesis of Flavanones from 2-Hydroxybenzoic Acids

摘要

The flavanones are mainly distributed in citrus fruits and have attracted considerable attention because they possess antioxidant effect, potent inhibition of cancer cell proliferation, and cytotoxic activity. The most frequently employed method for preparing flavanones involves the oxidative cyclization of 2'-hydroxychalcones. The treatment of 2'-hydroxychalcones with Co(salpr) in methanol under oxygen, K_3Fe(CN)_6 using phase transfer catalysis, and photochemical irradiation gives flavanones, but the yields are mostly low to moderate. 2'-Hydroxychalcones are also converted to flavanones by the treatment with acidic reagents such as H_2SO_4 in methanol, KF-celite in methanol, CF_3COOH, and polyphosphoric acid or basic reagents such as pyridine, KOH in methanol, and DBU in microwave irradiation, but most procedures are performed at high temperatures. Alternatively flavanones are prepared by the cyclization of 3-bromo-l-phenylprop-2-ynyl aryl ethers in the presence of Hg(OCOCF_3)_2 after NaBH_4 workup or the dehydration/cyclization of 3-hydroxy-1-o-hydroxyphen-yl-3-phenylpropan-l-ones derived from isoxazoles, but the former fails to furnish the methoxy substituted flavanones and the latter proceeds in four steps.