Stereoselective Synthesis of β-C-Glycosides of 3-Deoxy-d-manno-oct-2-ulosonic Acid (Kdo) via SmI2-Mediated Reformatsky Reactions

β-Stereoselective Kdo C-glycosylation by a (p-Tol)2SO/Tf2O preactivation strategy

There is very little research on the synthesis of β-3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) C-glycosides, which restricted their widespread application. Herein, a convenient and efficient approach to synthesize β-Kdo C-glycosides was developed based on a Tf2O/(p-Tol)2SO preactivation strategy using bench stable peracetylated Kdo thioglycoside as a donor via a thermodynamic SN1-like mechanism.

Ph3PO-Modulated Kdo Glycosidation for Stereoselective Synthesis of β-Kdo-Containing Disaccharides

A Ph3PO-modulated β-selective Kdo glycosidation approach is developed for the stereoselective synthesis of β-Kdo glycosides. With the readily available per-O-acetylated Kdo ynenoate as the donor, the glycosylation with a series of alcohols in the presence of Ph3PAuOTf and Ph3PO in toluene at low temperatures afforded the desired Kdo glycosides with good to excellent β-selectivities. Furthermore, the Ph3PO-modulated approach was effectively applied to the synthesis of β-(2→4)- and β-(2→8)-linked Kdo-Kdo disaccharides for further biological studies.

Additive-assisted synthesis of α-Kdo glycosides with peracetylated glycosyl ynenoate as a donor

A DMF-modulated glycosylation approach for the stereoselective synthesis of α-Kdo glycosides with readily accessible peracetylated Kdo ynenoate as a donor was described. By utilizing this approach, we completed the synthesis of various linkage types of Kdo-Kdo disaccharides and the α-Kdo-containing protected trisaccharide variant relevant to the lipopolysaccharide of Coxiella burnetii strain Nine Mile.

Recent advances on synthesis of C-glycosides

In recent years, C-glycosides have emerged as significant building blocks for many naturally occurring alkaloids and pharmaceutically active drug molecules. Therefore, significant efforts have been devoted to the construction of structurally important C-glycosidic linkages in carbohydrate compounds. Herein, we have summarized the recent developments of diverse synthesis of C-glycoside core between the time period from 2019 to 2022 focusing on different catalytic strategies, such as (i) transition-metal, and (ii) metal-free catalytic approaches. Further, the transition metal catalyzed C-glycosylations have been categorized into four sub classes: (a) metal based C-H activation, (b) cross-coupling reaction, (c) glycosyl radical intermediate-based process, and (d) Others.

Access to densely functionalized spirocyclopentenonyl oxindole frameworks via aza- and carbo-Piancatelli rearrangement

A new strategy for access to spirocyclopentenonyl oxindole frameworks is disclosed. Suitably anchored furfuryl alcohol at C3 of an oxindole was used for the aza-Piancatelli rearrangement, which furnished spirocyclic aminocyclopentenone frameworks with catalytic phosphomolybdic acid. The scope of the transformation was extended to the carbo-Piancatelli rearrangement with various indole derivatives.

Stereoselective gem-C,B-Glycosylation via 1,2-Boronate Migration

A novel protocol is established for the long-standing challenge of stereoselective geminal bisglycosylations of saccharides. The merger of PPh₃ as a traceless glycosidic leaving group and 1,2-boronate migration enables the simultaneous introduction of C-C and C-B bonds at the anomeric stereogenic center of furanoses and pyranoses. The power of this method is showcased by a set of site-selective modifications of glycosylation products for the construction of bioactive conjugates and skeletons. A scarce metal-free 1,1-difunctionalization process of alkenes is also concomitantly demonstrated.