Koenigs–Knorr reaction

The Koenigs- Knorr method by Wilhelm Koenig ( born April 22, 1851 in Dülken, † 1906) and his employee Eduard Knorr ( 1867-1926 ) is one of the most well-known reactions in carbohydrate chemistry and is used for the synthetic preparation of glycosides of monosaccharide derivatives.

The chemist Koenigs and Knorr treated in 1901 2,3,4,6 -tetra- O-acetyl- α -D - glucopyranosyl bromide ( acetobromoglucose ) in methanol with silver ( I) carbonate and received methyl-2, 3,4, 6- tetra-O -acetyl- β -D-glucopyranoside.

Reaction mechanism

In the first step, the glycosyl bromide reacts with silver elimination of silver bromide and the Silbercarbonatanion to the oxocarbenium ion. This is a Dioxolaniumion, which is attacked by methanol via a SN2 mechanism at the carbonyl carbon forms. By this attack it comes to inversion. After cleavage of a hydrogen atom ultimately arises the glycoside.

This reaction can also be applied to other carbohydrate protecting groups. In the synthesis of oligosaccharides, carbohydrates are used instead of methanol, which were modified with protective groups so that they only contain a "free" hydroxyl group.

The method was later transferred by Emil Fischer and Burckhardt Helferich to other chlorine-substituted purines and for the first time produced synthetically nucleosides. It was later further enhanced by numerous chemists and modified.