Stereoselective Synthesis of O-Glycosides with Borate Acceptors

Abstract

Borate esters have been applied widely as coupling partners in organic synthesis. However, the direct utilization of borate acceptors in O-glycosylation with glycal donors remains underexplored. Herein, we describe a novel O-glycosylation resulting in the formation of 2,3-unsaturated O-glycosides and 2deoxy O-glycosides mediated by palladium and copper catalysis, respectively. This O-glycosylation method tolerated a broad scope of trialkyl/triaryl borates and various glycals with exclusive stereoselectivities in high yields. All the desired aliphatic/aromatic O-glycosides and 2-deoxy O-glycosides were generated successfully, without the hemiacetal byproducts and O→C rearrangement because of the nature of borate esters. The utility of this strategy was demonstrated by functionalizing the 2,3-unsaturated glycoside products to form saturated β-O-glycosides, 2,3-deoxy O-glycosides, and 2,3-epoxy O-glycosides.

Stereoselective Synthesis of β-S-Glycosides via Palladium Catalysis

“…Subsequently, the utility of this strategy was demonstrated by functionalizing the 2,3-unsaturated β- S -glycoside products. As shown in Scheme b, the double bond of the unsaturated β- S -arylglycoside product 3aa can be hydrogenated by p -toluenesulfonyl hydrazide to give 2,3-dideoxy S -glycoside 8a in 86% yield . β- S -Arylglycoside 3aa could be dihydroxylated to form saturated β- S -alloside 9a in a yield of 67% under a condition of 5% potassium permanganate/magnesium sulfate aqueous solution at −20 °C .…”

Synthesis of Seven-Membered Ring Nucleosides and Serendipitous Simmons–Smith O-Glycosylation

“…Very recently, Yao and co-workers reported a parallel open-air Oglycosylation process that required palladium catalysts and aryl boronic acids. 20,21 To our knowledge, O-glycosylation of 1,2glycals under Simmons−Smith conditions, as carried out here, is unprecedented.…”