Exploring the Neighbouring Group Participatory Mechanism in Glycosylation Reaction

Glycosyl donors have been experimentally shown to have a high tendency for acyl transfer to the alcohol nucleophile as a major side product during glycosylation reactions. Therefore, a neighbouring group participatory mechanism of glycosylation is explored using D-galactopyranose based donor having 2-O-acyl functionality by employing density functional theory. The reaction proceeds via galactopyranosyl dioxolenium ion as a stable intermediate, which leads to the formation of α-glycoside 4, orthoester (5 or 6) and acyl transfer 7 as side products. The mechanism of the stereoselective formation of β-glycoside is investigated. Moreover, all the possible intermediates and transition states have been explored.