CONSTITUTION OF LUTEONE AND PARVISOFLAVONES-A AND PARVISOFLAVONES-B AND SYNTHESIS OF THEIR METHYL ETHERS AND RELATED ISOFLAVONES

The reaction of 5,7-dihydroxy-2′,4′-dimethoxyisoflavone (7) with 2-methylbut-3-en-2-ol in the presence of BF3-ether affords the 6-(3-methylbut-2-enyl) derivative (13) and its 8-isomer (9). Partial methylation of 7-hydroxy in (13) yields luteone trimethyl ether (15) and subsequent acid cyclisation gives α-isoluteone trimethyl ether (17) derived from natural luteone (3). Cyclodehydrogenation of (13) with DDQ followed by methylation afforded the fully methylated ether (19) of parvisoflavone-B, and the same two steps with (9) yielded the fully methylated ether (21) of parvisoflavone-A.