Corey House Reaction: Mechanism, Examples and Importance

Corey- House Reaction is also called as “coupling of alkyl halides with organometallic compounds' '. The four organic chemists who worked together and developed this significant reaction were E.J.Corey of Harvard University, Gary H. Posner of the Johns Hopkins University, G.M. Whitesides of MIT and Herbert O. House of the Georgia Institute of Technology. In wurtz reaction, formation of unsymmetrical alkanes is not possible but Corey-House reaction overcomes this reaction and thus, is suitable to use in the formation of alkane halide. 

Key Takeaways: Corey-House reaction, alkyl halide, Gilman reagent, wurtz reaction, lithium, alkanes, Corey-House synthesis, dialkyl lithium cuprate.

Also read: Precipitation Titration

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Corey-House Synthesis

Corey-House synthesis (also known as the Corey-Posner, Whitesides-House reaction and other permutations) is an organic reaction that involves the reaction of a lithium divinylcuprate with an alkyl halide to form a new alkane, an organocopper compound and a lithium halide.

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Mechanism

Alkyl halide reacts with Lithium metal, and solvated in dry ether to form alkyl lithium compound R-Li,

The R-X here can be primary, secondary or tertiary alkyl halide.

R-X + 2Li →R-Li + LiX

The second step involves the reaction of alkyl- lithium with cuprous iodide (CuI) to form lithium Dialkyl Cuprate .This reaction is known as Gilman Reagents.

2RLi + CuI → R₂CuLi +LiI

Finally, Dialkyl Cuprate lithium, when treated with the second alkyl halide (same or different alkyl halide) gives alkane.

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This reaction is known as Corey-House Synthesis.

 R′-X + R₂CuLi → R-R′ + R-Cu + LiX

In case the second alkyl halide is not the same with the first, then cross- products are formed i.e. R-R′. The other products i.e. R-R and R′-R′ are not formed in significant quantities. Therefore, for the reaction to work properly, it is important that the second alkyl halide must be methyl halide, benzyl halide, primary alkyl halide or secondary cycloalkyl halide. The alkanes formed here may be even, odd, symmetrical or unsymmetrical.

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Examples

Lithium dimethyl cuprate when reacts with ethyl bromide in presence of dry ether, it forms Propane along with lithium bromide and methyl copper.

(CH₃)₂CuLi + CH₃CH₂-Br → CH₃-CH₂-CH₃ + LiBr + CH₃-Cu

Here, Lithium dimethyl cuprate is prepared as follows:

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Methyl bromide (alkyl halide) reacts with lithium metal in the presence of dry ether and it forms methyl lithium and lithium bromide as bi-product.

CH₃-Br + 2Li → CH₃-Li + LiBr

Then methyl lithium is then treated with cuprous iodide to form lithium dimethyl cuprate, which is Gilman reagent

2(CH₃)-Li + CuI → (CH₃)₂CuLi + LiI

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Importance of Corey-House Reaction

1.The Corey- House reaction can be used for synthesis of all types of alkanes which may be straight chain or branched chain and may contain either even or odd number of carbon atoms. This reaction is mainly useful for synthesis of higher alkanes. Therefore this reaction is more suitable than the wurtz reaction.

2. High yields of alkanes can be obtained in Corey’s synthesis, especially when primary alkyl halide and primary, secondary or tertiary lithium dialkyl copper are used.
3. Corey’s synthesis is also useful for the synthesis of various organic compounds such as aldehydes, ketones and terminal alkynes.
4. The application of coupling partners, functional group tolerance and operational simplicity makes Corey-House synthesis the most powerful and practical tool for the synthesis of complex organic molecules. Moreover, it is also suitable at room temperature.

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Limitation

The main limitation of Corey-House synthesis is that it will be successful only when the alkyl group in alkyl halide is primary or secondary in nature.

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Things to Remember

1. The Corey-House synthesis is a three step process. When alkyl halide is treated with lithium metal and solvated in dry ether which converts alkyl halide to alkyl lithium compounds and when this alkyl lithium compound is treated with cuprous halide, it results in the formation of dialkyl lithium cuprate.
2. Reaction approach: Reagent used in this reaction is lithium metal and cuprous Iodine. The substrate can be two same or different alkyl halides. The methodology used in this reaction is the coupling reaction. Coupling actually takes place between lithium dialkyl cuprate and alkyl halide and the productivity here is hydrocarbons.
3. Vinyl and Phenyl Halide also couple with lithium dialkyl cuprate.

Ex. (CH₃CH₂CH₂CH₂)₂CuLi + Ph-I →Ph-CH₂-CH₂-CH₂-CH₃

4. It is important to note that this reaction works only alkyl halides are primary and secondary in nature. In tertiary alkyl halide the reaction does not take place due to the steric hindrance of three alkyl groups, sn2 reaction, substitution, due to which elimination may occur leading to the formation of side products.

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