Darzens reaction of 2‐bromo‐4,6‐dimethoxy‐3(2H)‐benzofuranone with aromatic aldehydes to form flavonoids

Abstract

The applicability of 2-bromo-4,6-dimethoxy-3(2H)-benzofuranone (1) to produce flavonoid-derived epoxides in the course of the Darzens reaction with aldehydes was investigated. However, instead of the epoxides, flavonols 3 and, in certain cases, benzofuranyl-substituted flavonols 4 were isolated. The generation of 3 is assumed due to a ring expansion of the initially formed epoxides. These flavonols can react with 1 to produce the unexpected 1:2 adducts 4 as minor products. The structure of the hexamethoxy derivative 4b (R 1 = H, R 2 = R 3 = OMe) was confirmed by X-ray crystallographic analysis.