Reagent-Controlled Divergent Synthesis of -Glycosides.

By turning on or switching off the directing effect of the C3-OH-located -diphenylphosphanylbenzoyl (-DPPB) group in glycals, a reagent-controlled protocol for divergent and regio- and stereoselective syntheses of -glycosides has been established. In particular, the silence of the directing effect of -DPPB was achieved by the introduction of a ZnCl additive, which is operationally simple and efficient. The flexibility of the novel protocol was exhibited not only by the easy access of both α- and β--glycosides but also by the versatility of the obtained formal Ferrier rearrangement products, which can be easily derivatized to various -glycoside analogues owing to the embedded multifunctionalities.