In this method, the glycosyl donor is protected at the C-2 position by an OAc group. The C-2-OAc protecting group is transformed into an enol ether by the Tebbe reagent (CpTi=CH), and then the glycosyl acceptor is tethered to the enol ether under acid-catalysed conditions to generate a mixed acetal. In a subsequent step, the β-mannoside is  formed upon activation of the anomeric leaving group (Y), followed by work up.