Rearrangement in the demethylation of 2'-methoxyflavones: Part II. Further experiments and the determination of the composition of lotoflavin

Abstract

Both 5 : 8 : 2' trimethoxyflavone (I ; R = Me) and the 2' : 3' : 6'- isomer(II; R = Me) yield 5 : 6 : 2' - trihydroflavone (IV : R = H) on demethylaction by hydridic acid. This result confirms previous views (see Gallagher et., al., J., 1953, 3770) that the diketone produced by decyclisation, e.g., (III) is intermediate in the rearrangement of both 5 : 8-dihydroxy- and 2' hydroxy- flavones. The presence of hydrogen ion is necessary for 5 : 8 → 5 : 6 rearrangement of flavones. Experiments related to the structure of lotoflavin, which Dunstan and Henry (Phil, Trans., 1901, 194, B, 515) thought to be 5 : 7 : 2' : 4' - tetra-hydroxyflavone (VI : R = H) have shown that 7 : 2' : 4' : 6'-tetramethoxy flavone (VI : R = Me) rearranges to form (V : R = H) on treatment with hydriodic acid. Lotoflavin as represented by the samples available is now found to be quercetin containing some kaempferol.