Auwers synthesis

The Auwers synthesis is a series of organic reactions forming a flavonol from a coumarone. This reaction was first reported by Karl von Auwers in 1908.



The first step in this procedure is an acid catalyzed aldol condensation between benzaldehyde and a 3-cyclooxapentanone to an o-hydroxychalcone. Bromination of the alkene group gives a dibromo-adduct which rearranges to the flavonol by reaction with potassium hydroxide.

Mechanism
A possible mechanism for the rearrangement step is shown below: