Reformatsky Reaction

* The Reformatsky reaction involves the treatment of an α-halo ester with zinc metal and subsequent reaction with aldehyde/ketone to get β- hydroxy ester.  

* Usually inert solvents like diethyl ether or THF are used in Reformatsky reaction.

* Better yields are obtained by using Zn-Cu couple or in situ preparation of zinc by reduction of zinc halides by potassium (also known as Rieke zinc).

Mechanism

* Initially zinc reacts with α-halo ester to give an organozinc reagent called reformatsky enolate. It is just like the Grignard reagent. It is added to the carbonyl group of aldehyde or ketone to furnish β- hydroxy ester.

* The organozinc reagents are less reactive and hence the nucleophilic addition to the ester group seldom occurs. Some of them are quite enough stable to be isolated and can be elucidated for the structure by techniques like X-ray analysis.

ILLUSTRATIONS

1) The following reaction is a classical example of Reformatsky reaction.

	Zn		H3O+
CH3CHO + Br-CH2-COOC2H5	----------------->		----------->	CH3CH(OH)-CH2COOC2H5
	Diethyl ether

2) The Reformatsky reaction is involved in the formation of  following β- hydroxy ester, which upon condensation gives Coumarin as the final product.