Stereoselective C-Glycosylation From Unsaturated Glycosyl Donors

C-Glycosides constitute a vital class of carbohydrate mimetics with enhanced metabolic stability, serving as key structural motifs in numerous bioactive molecules and natural products. While various synthetic approaches exist, the utilization of versatile unsaturated glycosyl donors (e.g., glycals, 4-keto-2,3-unsaturated glycosyl donors, ribals) offers a distinct and valuable platform for forging C-C bonds at the anomeric center with precise stereocontrol. This review provides a timely and comprehensive account of the stereoselective synthesis of C-glycosides from such unsaturated precursors, focusing on advances from 2020 to 2025. It systematically covers classical Ferrier-type rearrangements and state-of-the-art transition-metal-catalyzed cross-couplings employing palladium, cobalt, and nickel catalysts. Emerging strategies leveraging organocatalysts or dual-catalyst systems are also highlighted. For each methodology, the discussion emphasizes stereochemical outcomes, substrate scope, the mechanistic basis for stereoselectivity, and synthetic utility, highlighting applications in the construction and late-stage modification of complex glycosides and natural product analogs. This survey aims to underscore the unique advantages and future potential of unsaturated donors in the modular assembly of stereodefined C-glycosidic scaffolds.