Reformatsky reaction
The Reformatsky reaction is an organic reaction which condenses aldehydes or ketones with α-halo esters using metallic zinc to form β-hydroxy-esters:
The organozinc reagent, also called a 'Reformatsky enolate', is prepared by treating an alpha-halo ester with zinc dust. Reformatsky enolates are less reactive than lithium enolates or Grignard reagents and hence nucleophilic addition to the ester group does not occur. The reaction was discovered by Sergey Nikolaevich Reformatsky.
Some reviews have been published.
In addition to aldehydes and ketones, it has also been shown that the Reformatsky enolate is able to react with acid chlorides, imines, nitriles, and nitrones. Moreover, metals other than zinc have also been used, including magnesium, iron, cobalt, nickel, germanium, cadmium, indium, barium, and cerium. Additionally, metal salts are also applicable in place of metals, notably samarium(II) iodide, chromium(II) chloride, titanium(II) chloride, cerium halides such as cerium(III) iodide, and titanocene(III) chloride.
Structure of the reagent
The crystal structures of the THF complexes of the Reformatsky reagents tert-butyl bromozincacetate and ethyl bromozincacetate have been determined. Both form cyclic eight-membered dimers in the solid state, but differ in stereochemistry: the eight-membered ring in the ethyl derivative adopts a tub-shaped conformation and has cis bromo groups and cis THF ligands, whereas in the tert-butyl derivative, the ring is in a chair form and the bromo groups and THF ligands are trans. Note that, in contrast to lithium and boron enolates, which have the metals exclusively bond to oxygen, the zinc enolate moiety in the Reformatsky reagents have zinc atoms that are simultaneously O- and C-bound and can therefore be described as "organometallic".| ethyl bromozincacetate dimer | tert-butyl bromozincacetate dimer |