Question

In the following reaction, \( R _{2} CuLi \stackrel{ RX }{\longrightarrow} R - R ^{\prime}+ RCu + LiX \text {, the nature of } R \text { and } R ^{\prime} \text { should be } \)

• A. Any alkyl and 2⁰ Alkyl
• B. R= any alkyl; R¹=Methyl or alkyl or 2⁰ cycloalkyl
• C. R=1⁰ alkyl; R¹ = any alkyl
• D. R= any alkyl ; R¹= any alkyl

Answer 1

The correct option is B

R= any alkyl; R¹=Methyl or alkyl or 2⁰ cycloalkyl

The given reaction is Corey - house synthesis. An alkyl halides is first treated with Li metal in Dry ether to form alkyl lithium. This upon reaction with Cuprous iodide yields Lithium dialkyl cuprate.

$R-X\underset{dryether}{\overset{Li}{\to }}RLi+LiX$

$2RLi+Cul⟶Li(R{)}_{2}Cu+Lil$ (Lithium dialkyl cuprate)

Lithium dialkyl cuprate is known as Gilman reagent

$R^{\prime }X+R_{2}LiCu\underset{ether}{\overset{Dry}{\to }}{R}^{\prime }-R+RCu+LiX$

Foe Better yields,

R = any alkyl

R'= Methyl or Primary alkyl or secondary alkyl or secondary cycloalkyl or vinyl or aryl

In other words , R'X should not be a tertiary alkyl halide.