Darzens

Darzens refers to a class of chemical reactions known as the Darzens condensation or Darzens glycidic ester condensation. This reaction involves the condensation of an aldehyde or ketone with an alpha-haloester in the presence of a base. The result is the formation of an alpha,beta-epoxy ester, also known as a glycidic ester.

The reaction is typically carried out using a strong base such as sodium ethoxide or potassium tert-butoxide. The base deprotonates the alpha-haloester, forming a carbanion that then attacks the carbonyl carbon of the aldehyde or ketone. This is followed by an intramolecular displacement of the halide ion by the alkoxide intermediate, leading to the formation of the epoxide ring.

Glycidic esters produced by the Darzens condensation are versatile synthetic intermediates. They can be hydrolyzed to form glycidic acids, which upon decarboxylation yield aldehydes or ketones. This transformation is known as the Darzens rearrangement. Alternatively, the epoxide ring can be opened under various conditions to introduce other functional groups. The Darzens condensation is a valuable tool in organic synthesis for the construction of complex molecules, including pharmaceuticals and natural products. The reaction was first reported by the French chemist Auguste Darzens in 1904.