Carbohydrates play essential roles in various physiological and pathological processes. Trifluoromethylated compounds have wide applications in the field of medicinal chemistry. Herein, we report a practical and efficient trifluoromethylation of glycals by an electrochemical approach using CF3SO2Na as the trifluoromethyl source and MnBr2 as the redox mediator. A variety of trifluoromethylated glycals bearing different protective groups are obtained in 60–90% yields with high regioselectivity. The successful capture of a CF3 radical indicates that a radical mechanism is involved in this reaction.

C-Glycosides are a class of carbohydrates with a variety of biological activities, and the construction of their unique C-C glycosidic bond is a hot and challenging topic in carbohydrate chemistry. The formation of new C-C bond from carbon-carbon double bond is a common strategy in organic chemistry. With the rapid development of ene-chemistry, great progress in the synthesis of C-glycosides from glycal donors containing 1,2-double bond has been made. In this review, the methods for the synthesis of C-glycosides based on glycals are summarized, including Ferrier I-type C-glycosylation, Heck-type C-glycosylation, C-glycosylation of 1-substituted glycals using transition metal-catalyzed coupling reaction, Michael-type C-glycosylation of 2-substituted glycals, and radical addition type C-glycosylation of glycals. Keywords glycal; C-glycoside; C-glycosylation; carbohydrate 碳苷是指糖上端基碳原子和配糖体通过碳-碳键相 连的糖类化合物. 自然界存在的天然碳苷化合物多具有 重 要 的 生 理 活 性 . 假 尿 嘧 啶 核 苷 [1] (pseudouridine) (Scheme 1)是第一个被报道的碳核苷. 它被认为是 tRNA 降解的最终产物, 在肿瘤患者体内含量会异常增高, 可 以作为肿瘤标志物. 从中药葛根中分离得到的异黄酮类 碳苷葛根素 [2] (puerarin), 具有舒张血管、缓解心绞痛等 多种活性. 很多具有重要生理活性的天然产物也含有碳 苷单元, 比如 Kendomycin [3] . 与氧苷的 C-O 键相比, 碳苷端基的 C-C 键对酶和化学(酸)水解有更强的耐受 性. 例如, α-半乳糖神经酰胺 KRN7000 的碳苷类似物对 小 鼠 B16 黑色 素瘤 细胞的 保护 作用比 其氧 苷母体 KRN7000 强 1000 倍 [4] ; 由根皮苷(phlorizin)改造后的碳

Herein, the convenient one-step electrochemical bromination of glycals using Bu4NBr as the brominating source under metal-catalyst-free and oxidant-free reaction conditions was described. A series of 2-bromoglycals bearing different electron-withdrawing or electron-donating protective groups were successfully synthesized in moderate to excellent yields. The coupling of tri-O-benzyl-2-bromogalactal with phenylacetylene, potassium phenyltrifluoroborate, or a 6-OH acceptor was achieved to afford 2C-branched carbohydrates and disaccharides via Sonogashira coupling, Suzuki coupling, and Ferrier rearrangement reactions with high efficiency. The radical trapping and cyclic voltammetry experiments indicated that bromine radicals may be involved in the reaction process.

A novel glycosylation protocol has been established by using N-(glycosyloxy)acetamides as glycosyl donors. The N-oxyacetamide leaving group in donors could be rapidly activated in the presence of Cu(OTf) or SnCl under microwave irradiation. This glycosylation process afforded the coupled products in high yields, and the reaction enjoyed a broad substrate scope, even for disarmed donors and hindered acceptors. The easy availability of the donors, the high stability of N-(glycosyloxy)acetamides, and the small leaving group make this method very practical.