Palladium‐Catalyzed Regioselective and Diastereoselective C ‐Glycosylation by Allyl‐Allyl Coupling

Cobalt-Catalyzed versus Base-Promoted Skeletal- and Stereodivergent Synthesis of Bicyclic α-C-, β-O-, and α-O-Glycosides

A stereodivergent synthesis of bicyclic α-C-, β-O-, and α-O-glycosides is achieved with nonprecious Co(dpm)3, K2CO3, and DBU, respectively. Cobalt-catalyzed decarboxylative allylation of 2,3-unsaturated 4-keto glycosyl carbonates with 1,3-diketones delivers α-C-glycosides in good yields with exclusive chemo- and regiocontrol and excellent diastereoselectivity (>20:1 dr). K2CO3 enables β-O-glycosides via a cascaded intermolecular Michael addition/SN2-like cyclization, whereas DBU promotes further C5 epimerization to give α-O-glycosides. Mechanistic studies (deuterium labeling and intermediate capturing) validate the pathways. Gram-scale synthesis and late-stage functionalization of pharmaceuticals demonstrate practicality.

Palladium-Catalyzed Stereospecific Glycosylation Enables Divergent Synthesis of N-O-Linked Glycosides

We present a versatile palladium-catalyzed glycosylation platform that enables facile access to structurally diverse N-O-linked glycosides with constantly excellent regio- and stereoselectivities. Importantly, this approach offers a broad substrate scope, low catalyst loadings, and outstanding chemoselectivity, allowing for the selective reaction of oximes/hydroximic acids over hydroxyl groups that would otherwise pose challenges in conventional glycosylation methods. The synthetic utility of this method is further exemplified through a range of synthetic transformations and late-stage modification of bioactive molecules. Overall, our method provides an efficient toolkit for the synthesis of N-O-linked glycosides, which will facilitate their subsequent biological evaluations.

Developments in the stereoselective synthesis of benzopyran, benzopyrone and flavonoid based natural product analogues using C-glycosides as an intrinsic chiral synthon

Stereoselective synthesis is essential for propelling mainstream academia toward a relentless pursuit of novel and cutting-edge strategies for constructing molecules with unparalleled precision. Naturally derived benzopyrans, benzopyrones, and flavonoids are an essentially prominent group of oxa-heterocycles, highly significant targets in medicinal chemistry owing to their extensive abundance in biologically active natural products and pharmaceuticals. The molecular complexity and stereoselectivity induced by heterocycles embedded with C-glycosides have attracted considerable interest and emerged as a fascinating area of research for synthetic organic chemists. This present article emphasizes the existing growths in the strategies involving the diastereoselective synthesis of C-glycosylated benzopyrans, benzopyrones, and flavonoids using naturally acquired glycones as chiral synthons.

De novo asymmetric Achmatowicz approach to oligosaccharide natural products

The development and application of the asymmetric synthesis of oligosaccharides from achiral starting materials is reviewed. This de novo asymmetric approach centers around the use of asymmetric catalysis for the synthesis of optically pure furan alcohols in conjunction with Achmatowicz oxidative rearrangement for the synthesis of various pyranones. In addition, the use of a diastereoselective palladium-catalyzed glycosylation and subsequent diastereoselective post-glycosylation transformation was used for the synthesis of oligosaccharides. The application of this approach to oligosaccharide synthesis is discussed.

Reagent-Controlled Regiodivergent Annulations of Achmatowicz Products with Vinylogous Nucleophiles: Synthesis of Bicyclic Cyclopenta[b]pyrans and 8-Oxabicyclo[3.2.1]octane Derivatives

Two reagent-controlled regiodivergent annulation protocols for Achmatowicz products with vinylogous nucleophiles have been developed, which furnished a series of bicyclic cyclopenta[b]pyrans and 8-oxabicyclo[3.2.1]octane derivatives in 28-90% yields. Plausible mechanisms were proposed to involve either Pd-catalyzed Tsuji-Trost allyl-allyl coupling and concomitant Michael cyclization or quinine-promoted cascade stepwise [5 + 2] cycloaddition and intramolecular Michael cyclization.