Synthetic studies on flavone derivatives. XIV. Synthesis of 2',4',5'-trioxygenated flavones.

Seven naturally occurring flavones oxygenated at C-2', C-4' and C-5' in ring B were synthesized, together with their isomers, to confirm the proposed structures. The synthesized flavones 1, 2, 3a, 5, 7 and 8 were identical with the corresponding natural flavones, but 4a was not. The spectral properties of these flavones are discussed.