In summary, an efficient total synthesis of Nigrasin I and
Kuwanon C, two biologically interesting natural flavonoids with
distinct regioisomeric isoprenyl side chains, has been realized for
the first time starting from commercially available 1-(2,4,6-
trihydroxyphenyl)ethanone via a linear reaction sequence of 11
steps in the overall yields of 22% and 21%, respectively. The application
of HCOONH4/Lindlar catalyst instead of PdeC as the
debenzylation condition and the Claisen rearrangement of the
allylated 16 featured the synthetic strategy. The use of acetic anhydride
as the solvent and the employment of microwave irradiation
are disclosed to be critically important in the efficient and
selective Claisen rearrangement. The present synthetic strategy has
provided a facile and practical synthesis of isoprenylated flavonoids,
Nigrasin I and Kuwanon C, and thus might stimulate the
future research on the bioactivity of these molecules.