Electrochemical Epoxidation and Carbon-Carbon Bond Cleavage for the Preparation of 3-Methyl-4-oxo-2-phenyl-4H-1-benzopyran-8-carboxylic Acid from 3-Methyl-2-phenyl-8-(1-propenyl)-4H-1-benzopyran-4-one

Article abstract of DOI:10.1246/bcsj.58.2361

Electrooxidative carbon-carbon bond cleavage is useful for the preparation of 3-methyl-4-oxo-2-phenyl-4H-1-benzopyran-8-carboxylic acid (1b) from 3-methyl-2-phenyl-8-(1-propenyl)-4H-benzopyran-4-one (2).Olefin 2 was transformed into 3-methyl-8-(1,2-epoxypropyl)-3-methyl-2-phenyl-4H-1-benzopyran-4-one (3) by the electrochemical bromohydrination in an MeCN-H2O-H2SO4-NaBr-(Pt) system followed by treatment of aqueous sodium hydroxide (94percent).The epoxide 3 was electrooxidized in an MeOH-H2SO4-(C) system, affording 8-formyl-3-methyl-2-phenyl-4H-1-benzopyran-4-one (4) in 83percent yield.Hydrogen peroxide oxidation of 4 in refluxing 2-butanone gave 1b in 86percent yield.