High-Yield Total Synthesis of (−)-Strictinin through Intramolecular Coupling of Gallates

This paper describes a total synthesis of (−)-strictinin, an ellagitannin that is 1-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl (HHDP)-β-d-glucose. In the study, total efficiency of the synthesis was improved to produce a 78% overall yield in 13 steps from d-glucose. In the synthesis, formation of the 4,6-(S)-HHDP bridge including the 11-membered bislactone ring was a key step, in which intramolecular aryl–aryl coupling was adopted. The coupling was oxidatively induced by CuCl2–n-BuNH2 with perfect control of the axial chirality, and the reaction conditions of this coupling were optimized thoroughly to achieve the quantitative formation of the bridge.