Cooperativity and anticooperativity in anomeric systems

Cooperativity/competUion among acceptors (armed/disarmed carbohydrates) Cleavage of the C-X bond at the anomeric position proceeds via evolution of the anomeric n o C-X interaction that culminates in the oxocarbenium ion. This carbocation is so strongly stabilized by n j- p interaction that this interaction is commonly described as a dative it-bond. Because oxacarbenium ions are strongly stabilized, their formation is relatively facile. In cross-coupling glycosylalion reactions, however, it is beneficial to differentiate the reactivity of two saccharides for the selectivity reasons. The competition and cooperativity between stereoelectronic effects can be used to fine-tune the reactivity of anomeric systems. 

Concept Anomeric stabilization makes cation formation (no  

A destabilizing a-acceptor next to the oxacarbenium ion modulates stability and reactivity 

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