[Au]/[Ag]-Catalyzed Glycosidation of Ethynylcyclohexyl Glycosyl Carbonates Enables\nDirect Stereoselective Synthesis of 2‑Azido-2-deoxy-β-mannopyranosides

We\ndescribe the [Au]/[Ag]-catalyzed activation of ethynyl­cyclohexyl\n2-azido-4,6-<i>O</i>-benzylidene mannosyl carbonates for\nβ-mannosamine linkage preparation in high yield and selectivity\nin a temperature- and concentration-dependent manner. VT-NMR studies\nreveal an anomeric triflate intermediate generated in the absence\nof an acceptor alcohol that is stable up to −10 °C. The\ngenerality of the protocol was illustrated by successful application\nto a series of acceptors and by synthesis of a fully protected <i>Streptococcus pneumoniae</i> type 19F capsular trisaccharide.