Recent Chemical Advances in C-Glycosidic Ellagitannins

C-Glycosidic ellagitannins are a complex subclass of hydrolyzable tannins characterized by a carbon-carbon bond between the C-1 position of an open-chain d-glucose core and a hexahydroxydiphenoyl unit. Their architectures, featuring densely packed oxygen functionalities, multiple axes of chirality, and unique C-glycosidic linkages, render them formidable total-synthesis targets. This review traces the biomimetic strategies inspired by the biosynthetic pathways proposed in recent chemical advances. Key milestones include site- and atroposelective oxidative coupling for constructing hexahydroxydiphenoyl and nonahydroxytriphenoyl units, and stereoselective C-glycosidic bond formation through pyranose ring-opening methodologies, particularly the transition from the multistep Wittig olefination to the oxime-based formyl surrogates that offer direct thermodynamic control and complete stereoselectivity. Finally, the application of these methodologies to divergent analog synthesis and multi-unit architectures through robust double and triple C-glycosylations is discussed, which establishes a practical platform for accessing higher-order ellagitannin oligomers.