Stereoselective Synthesis of <i>O</i>-Glycosides with Borate Acceptors
Xiaoxiao Zhao, Zhentao Zhang, Jing Xu, Nengzhong Wang, Nianyu Huang, Hui Yao
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 2-deoxy 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.