Syntheses of Ring-substituted Flavonoids and Allied Compounds. XI. Synthesis of Hinokiflavone

Abstract

Permethylated 3-nitrobisflavonyl ether (XXIV), the key-intermediate for the synthesis of the proposed structure (XXX), was prepared by the condensation of 8-hydroxy-4', 5, 7-trimethoxyflavone (XX) with 4'-iodo-3'-nitro-5, 7-dimethoxyflavone (XXIII) in DMSO in the presence of K₂CO₃ at 110°for 1 hr. The nitro ether was reduced by Na₂S₂O₄ in aq. DMF, diazotized and decomposed with 50% H₃PO₂ to give XXVII, which proved to be different from pentamethyl ether of natural hinokiflavone. An alternative bisflavone with 4', 6''-coupling positions has now been synthesized in a similar route described above. XXXIV was condensed with XXIII to 3'-nitro ether (XXXV), which was reduced, diazotized and decomposed to give permethylated ether (XXXVIII), identical with permethyl ether of natural hinokiflavone. The synthesized methyl ether was finally demethylated by means of HI·Ac₂Oat 130-140° for 3 hr to give 4''', 5, 5'', 7, 7'-pentahydroxy-4', 6''-bisflavonyl ether (XLII) identical with natural hinokiflavone. 4', 8''-Bisflavone (XXVII) was converted into a bisflavone (XLII) identical with natural hinokiflavone, when heated with HI·Ac₂O as above (Wessely-Moser rearrangement).