Synthesis of icariin from kaempferol through regioselective methylation and para-Claisen-Cope rearrangement

The hemisynthesis of the naturally occurring bioactive flavonoid glycoside icariin (1) has been accomplished in eleven steps with 7% overall yield from kaempferol. The 4'-OH methylation of kaempferol, the 8-prenylation of 3-O-methoxymethyl-4'-O-methyl-5-O-prenyl-7-O-benzylkaempferol (8) via para-Claisen-Cope rearrangement catalyzed by Eu(fod)(3) in the presence of NaHCO3, and the glycosylation of icaritin (3) are the key steps.