Regioselective synthesis of prenylisoflavones. Syntheses of allolicoisoflavone A, 2,3-dehydrokievitone, and related compounds

Article abstract of DOI:10.1246/bcsj.71.2673

The palladium-catalyzed coupling reaction of 2',4',5,7- tetrakis(benzyloxy)-5'-iodolsoflavone (12), synthesized from the 5- iodochalcone 9, with 2-methyl-3-butyn-2-ol gave the corresponding 5'-(3- hydroxy-3-methyl-1-butynyl)isoflavone 13. The catalytic hydrogenation of 13 gave 2',4',5,7-tetrahydroxy-5'-(3-hydroxy-3-methylbutyl)isoflavone (2). Dehydration of the benzoate 14 of 2 afforded a mixture of 5'-(3-methyl-2- butenyl)isoflavone 15 and the isomer 5'-(3-methyl-3-butenyl)isoflavone 16. The separation of 15 was accomplished by a treatment of the mixture (15 and 16) with mercury(II) nitrate. Hydrolysis of 15 afforded 2',4',5,7- tetrahydroxy-5'-prenylisoflavone (allolicoisoflavone A) (1). In a similar manner, 2',4',5,7-tetrahydroxy-8-prenylisoflavone (2,3-dehydrokievitone) (3) and 2',4',5,7-tetrahydroxy-8-(3-hydroxy-3-methylbutyl)isoflavone (2,3- dehydrokievitone hydrate) (4) were synthesized from the corresponding 8- iodoisoflavone 22. The tetramethyl ether 5 of 3 was also prepared from the 8- iodotetramethoxyisoflavone 32.