Organocatalytic Glycosylation by Using Electron-Deficient Pyridinium Salts

A new organocatalytic glycosylation method based on electron‐deficient pyridinium salts is reported. At ambient temperature and catalyst loadings as low as 1 mol %, 2‐deoxyglycosides were formed from benzyl‐ and silyl‐protected glycals and primary or secondary glycosyl acceptors, with excellent yields and anomeric selectivity. Mechanistic investigations point to alcohol–pyridinium conjugates (1,2‐addition products) as key intermediates in the catalytic cycle. Less is more! Electron‐deficient pyridinium cations efficiently catalyze the glycosylation of benzyl‐ and silyl‐protected glycals. Both primary and secondary alcohols can act as glycosyl acceptors. The glycosylation shown proceeds at RT and affords exclusively the α‐galactoside. The 1,2‐addition product of the alcohol component to the pyridinium cation most likely acts as crucial catalysis intermediate.