Koenigs–Knorr reaction

In its original form, Koenigs and Knorr treated acetobromoglucose with alcohols in the presence of silver carbonate.

Esters (e.g. acetyl, benzoyl, pivalyl) generally provide good anchimeric assistance, whereas ethers (e.g. benzyl, methyl etc.)

From this structure a dioxolanium ring is formed, which is attacked by methanol via an SN2 mechanism at the carbonyl carbon atom.

After deprotonation of the intermediate oxonium, the product glycoside is formed.

The method was later transferred by Emil Fischer and Burckhardt Helferich to other chloro-substituted purines and produced thus for the first time synthetic nucleosides.