A Short On Preparation Of Alkanes By Corey- House Synthesis

The Corey–House synthesis (also known as the Corey–Posner–Whitesides–House reaction and other variations) is an organic reaction in which a lithium divinylcuprate (R₂CuLi) reacts with an organic pseudohalide (RX) to produce, byproducts include a novel alkane, an unidentified organocopper molecule, and lithium halide.

In theory, a carbanion equivalent such as an organolithium or Grignard reagent can generate a new carbon–carbon bond by reacting directly (without copper) with an alkyl halide in a nucleophilic substitution reaction. Aside from the usage of metal acetylides as nucleophiles, however, due to metal–halogen exchange and/or the creation of substantial amounts of reduction or elimination side-products, such a procedure rarely works well in practice. The Corey–House reaction is a generic and high yielding technique for connecting two alkyl groups or an alkyl group and an aryl group as a solution to this problem.

The Mechanism and Process Of Reaction

Two preliminary steps are required to create the required Gilman reagent from an alkyl halide for the Corey-House synthesis. To make an alkyl lithium reagent, RLi, the alkyl halide is first reacted with lithium metal in dry ether. For the lithiation stage, the initial alkyl halide can be a primary, secondary, or tertiary alkyl chloride, bromide, or iodide:

The alkyl lithium is then treated with copper(I) iodide (CuI) in a transmetalation reaction to produce a lithium dialkylcuprate, commonly known as a Gilman reagent (named after Henry Gilman of Iowa State University):

If functional group incompatibility prevents the use of alkyllithium reagents, transmetalation from other metals (e.g., Mg, Zn, Al, B) may be considered as an alternative for the synthesis of the organocopper reagent.

The reaction between the organocopper reagent, usually a lithium dialkylcuprate as made above, and a second alkyl (pseudo)halide or an aryl iodide is known as the Corey-House synthesis. A C–C bond is formed between the two organic pieces as a result of this in the most typical version of the Corey–House synthesis, one equivalent of the R group is squandered as an ill-characterised alkyl copper molecule (possibly polymeric; normally converted to RH following aqueous workup), as shown by the stoichiometry. To circumvent this in circumstances where R is a valuable or complicated fragment, a reagent (R)(RU)CuM can be synthesised and utilised instead, where RU is an non transferable dummy ligand (e.g., RU = cyano, alkynyl, 2-thienyl, etc.).

When R and R’ differ, only the cross product R–R’ is formed; R–R or R’–R’ do not form in meaningful proportions. As a result, the Corey–House reaction is a cross-coupling reaction. One of the earliest transition metal-mediated (or catalysed) cross-coupling processes to be found is the Corey–House synthesis.

When a configurationally pure alkyl electrophile is utilised with alkyl bromides and tosylates, inversion of configuration occurs. The reaction is thought to work by an SN2-like mechanism to produce a copper(III) species, which is then reductively eliminated to produce the coupling product. When alkyl iodides with an olefin tether are utilised, configuration scrambling is observed, as well as the formation of cyclisation products, both of which indicate the presence of radicals.

It’s vital to remember that the alkyl (pseudo) halide coupling partner must be methyl, benzylic, allylic, 1° alkyl, or 2° cycloalkyl for this reaction to work. 3° and acyclic 2° electrophiles produce disappointing outcomes in the majority of cases.

What Is The Significance Of Corey House’s Reaction?

The process of synthesising an organic compound takes only a few minutes and takes place at room temperature. The product is easily available as a result of this reaction. It is a highly effective method for cross-coupling organic molecules. The preparation of novel alkanes is a common application of this reaction. This reaction is more efficient in producing straight-chain, branched-chain, symmetrical, and unsymmetrical alkanes. Primary alkyl halides are employed to provide better results. Because of the number of carbons prepared, the Corey House reaction has an advantage over the Wurtz reaction.

Lithium Dialkyl Cuprates

The reaction of two equivalents of an organolithium with a copper (I) halide produces lithium dialkyl cuprates.

Anhydrous diethyl ether or tetrahydrofuran are common solvents. In most cases, the alkyl group is predominant. Decomposition is a problem in secondary and tertiary schools.

Alkyl Chloride

Alkyl halides, also known as haloalkanes, are created when hydrogen atoms in an aliphatic hydrocarbon are replaced with halogen atoms such as fluorine or chlorine. When an H-atom in an alkane molecule is replaced with a Chlorine atom, alkyl chloride is formed.

Example

C₂H₆ + Cl₂ → C₂H₅Cl + HCl

Conclusion

The Corey-House synthesis (also known as the Corey-Posner, Whitesides-House, and other variants) is an organic reaction in which a lithium divinylcuprate reacts with an alkyl halide to produce a new alkane, an organocopper molecule, and a lithium halide.

We can only make even carbon number alkanes with the Wurtz reaction, while we can make odd and even carbon number alkanes with the Corey House reaction.

As a result, the corey house reaction is preferable to the Wurtz reaction.