Homoisoflavonoids are in the subclass
of
the larger family of flavonoids but have one more alkyl carbon than
flavonoids. Among them, 5,7,8-trioxygenated homoisoflavonoids have
not been extensively studied for synthesis and biological evaluation.
Our current objective is to synthesize 2 5,7,8-trioxygenated chroman-4-ones
and 12 5,7,8-trioxygenated homoisoflavonoids that have been isolated
from the plants Bellevalia eigii, Drimiopsis maculata, Ledebouria graminifolia, Eucomis autumnalis, Eucomis punctata, Eucomis pallidiflora, Chionodoxa luciliae, Muscari comosum, and Dracaena cochinchinensis. For this purpose, 1,3,4,5-tetramethoxybenzene and 4′-benzyloxy-2′,3′-dimethoxy-6′-hydroxyacetophenone
were used as starting materials. Asymmetric transfer hydrogenation
using Noyori’s Ru catalyst provided 5,7,8-trioxygenated-3-benzylchroman-4-ones
with R-configuration in high yield and enantiomeric excess. By selective
deprotection of homoisoflavonoids using BCl3, the total
synthesis of natural products including 10 first syntheses and three
asymmetric syntheses has been completed, and three isomers of the
reported dracaeconolide B could be provided. Our research on 5,7,8-trioxygenated
homoisoflavonoids would be useful for the synthesis of related natural
products and pharmacological applications.