Flavonoids synthesis. I. Synthesis and spectroscopic properties of flavones with two hydroxy and five methoxy groups at C-2',3',4',5,6,6',7 and C-2',3,4',5,5',6,7.

Four flavones oxygenated at C-2', 3', 4' and 6', and seven flavonols oxygenated at C-2', 4' and 5', each with a 5, 6, 7-trioxygenated structure in ring A, were synthesized for comparison with brickellin and apulein. The structures of brickelin and apulein were thus confirmed to be 2', 5-dihydroxy-3, 4', 5', 6, 7-pentamethoxyflavone and 2', 5'-dihydroxy-3, 4', 5, 6, 7-pentamethoxyflavone, respectively. The differences between flavones oxygenated at 2', 3', 4' and 6', and flavonols oxygenated at C-2', 4', 5' are discussed on the basis of spectroscopic data.