Cationic zirconocene- or hafnocene-based Lewis acids in organic synthesis: glycoside–flavonoid analogy

Cationic metallocene species, generated from Cp2MCl2 and AgClO4 (M=Zr, Hf), were used for the glycosylation of catechin derivative , enabling a concise synthesis of a glycosyl flavonoid, astilbin (). Further study revealed the efficiency of this Lewis acidic species for SN1-type activation of the C(4) position of catechin derivative , enabling selective substitution with various nucleophiles.