Venturing beyond Donor-Controlled Glycosylation: New Perspectives toward Anomeric Selectivity.

Glycans are complex compounds consisting of sugars linked glycosidically, existing either as pure polysaccharides or as part of glycoconjugates. They are prevalent in nature and possess important functions in regulating biological pathways. However, their diversity coupled with physiochemical similarities makes it challenging to isolate them in large quantities for biochemical studies, hence hampering progress in glycobiology and glycomedicine.

Asymmetric syntheses of 8-oxabicyclo[3,2,1]octane and 11-oxatricyclo[5.3.1.0]undecane from glycals.

Herein, we describe an efficient method to prepare enantiomerically pure 8-oxabicyclo[3.2.1]octanes gold(i)-catalyzed tandem 1,3-acyloxy migration/Ferrier rearrangement of glycal derived 1,6-enyne bearing propargylic carboxylates.

Palladium-Catalyzed Decarboxylative Allylation/Wittig Reaction: Substrate-Controlled Synthesis of C-Vinyl Glycosides.

A palladium-catalyzed one-pot Tsuji-Trost type decarboxylative allylation/Wittig reaction has been developed to synthesize C-vinyl glycosides. Screening of various aldehydes led to formation of β,(E)-selective C-vinyl glycosides with pyridyl group containing aldehydes and β,(Z)-selective C-vinyl glycosides with nonpyridyl aldehydes. A plausible mechanism is proposed based on the coordination effect of the aldehydes.

The first intermolecular interrupted imino-Nazarov reaction: expeditious access to carbocyclic nucleoside analogues.

The analogous imino-variant of the Nazarov reaction suffers from unfavorable energetics associated with the ring closure process, thereby limiting the utility of this class of reactions. In this report, the realization of the first intermolecular interrupted imino-Nazarov reaction utilizing silylated pyrimidine derivatives as nucleophilic trapping partners culminated in an expedient synthetic route to carbocyclic nucleoside analogues. The potential application of silylated nucleobases to intercept the oxyallyl cation in other variants of the Nazarov reaction provides vast opportunities to develop new strategies for the formation of carbocyclic nucleoside analogues.

Palladium-catalyzed glycosylation: novel synthetic approach to diverse N-heterocyclic glycosides.

An efficient and highly stereoselective method for the construction of N-heterocyclic glycosides is reported. This method is based on a palladium-catalyzed allylation which proceeded to provide N-heterocyclic glycosyl compounds in good-to-excellent yields with β- or α-selectivity. Various N-nucleophiles were examined for this reaction and selected N-glycosyl isatin substrates were further elaborated to bis-indole sugars which have potential as antiproliferative drugs.

Intramolecular C - N bond formation under metal-free conditions: synthesis of indolizines.

Polysubstituted indolizine derivatives are constructed via intramolecular CN bond formation/CH bond cleavage under metal-free conditions. These methods offer straightforward pathways to transform pyridyl chalcones into a variety of indolizines.

A highly efficient dual catalysis approach for C-glycosylation: addition of (o-azaaryl)carboxaldehyde to glycals.

A novel and efficient dual catalysis approach by concurrent activation of glycals and (o-azaaryl)-carboxaldehydes using palladium and N-heterocyclic carbene has been developed. The two electrophiles could react after activation through formation of the Breslow intermediate and a π-allyl Pd complex, widening the scope of reacting glycosylation partners and opening up possibilities for future glycosylation.