Figure 5: Syntheses of the valoneoyl (a) and tergalloyl (b) groups.
From: A unified strategy for the synthesis of highly oxygenated diaryl ethers featured in ellagitannins
The sequence developed for the synthesis of the DHDG group—that is, oxa-Michael addition to 7-Br, elimination and reductive aromatization—was applied to the synthesis of the valoneoyl and tergalloyl groups. These successful syntheses showed that the sequence was a unified method for the synthesis of C–O digallates. The intramolecular coupling of 28 is the first HHDP synthesis starting from unequally protected gallates. For structures of 29 and 30, see Supplementary Methods 35 and 36. Bu, butyl; DDQ, 2,3-dichloro-5,6-dicyano-p-benzoquinone; Nap, 2-naphthylmethyl; Pr, propyl.
