The armed–disarmed concept

The armed–disarmed concept refers to the relative ease
or difficulty of activating a sugar as a glycosyl donor in
glycosylation reactions.1 Disarmed glycosyl donors have
highly electron withdrawing protecting groups (e.g., esters,
amides) that destabilize the formation of the oxycarbenium
ion/ion pair2 during the course of the glycosylation,
whereas less electron withdrawing protecting groups (e.g.,
ethers) are less destabilizing and therefore arm the glycosyl
donor.

Tetrahedron Letters 49 (2008) 2546–2551