Koenigs–Knorr reaction

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

[1] Shortly afterwards Fischer and Armstrong reported very similar findings.

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.

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.