Studies of the Selective O-Alkylation and Dealkylation of Flavonoids. 10. Selective Demethylation of 7-Hydroxy-3,5,8-trimethoxyflavones with Anhydrous Aluminum Halide in Acetonitrile or Ether

Article abstract of DOI:10.1021/jo00230a009

Demethylation of five 7-hydroxy-3,5,8-trimethoxyflavones and their acetates with anhydrous aluminum halides in acetonitrile or ether was studied and the following results were found. (1) The demethylation was apparently influenced by both solvents and afforded 5,7-dihydroxy-3,8-dimethoxyflavones in acetonitrile and 3,7-dihydroxy-5,8-dimethoxyflavones in ether as main products. (2) The demethylation with 5percent w/v anhydrous aluminum bromide in acetonitrile procedeed quantitatively to give a mixture of corresponding 5- and 3-hydroxyflavones, but that of 7-hydroxy-3,4',5,8-tetramethoxyflavone and its acetate with 10percent anhydrous aluminum chloride in acetonitrile afforded 6-acetyl-5,7-dihydroxy-3,4,8-trimethoxyflavone as a byproduct along with the 5- and 3-hydroxyflavones. (3) The demethylation of the acetates proceeded more smoothly than that of hydroxyflavones and was superior to that of the flavones with a hydroxy group. (4) These demethylations are available for the syntheses of 3- or 5-hydroxyflavones with no substituent at 6-position.