Question

Show how to convert 1-bromopentane to each of these compounds using a lithium diorganocopper (Gilman) reagent. Write an equation, showing structural formulas, for each synthesis. (a) Nonane (b) 3 -Methyloctane (c) 2,2 -Dimethylheptane (d) 1-Heptene (e) 1-Octene

Short answer

Question: Convert 1-bromopentane to the following compounds using a lithium diorganocopper (Gilman) reagent and provide the reaction conditions: (a) Nonane (b) 3-Methyloctane (c) 2,2-Dimethylheptane (d) 1-Heptene (e) 1-Octene Answer: (a) Use lithium di-n-butyylcopper (LiCuBu₂) as the Gilman reagent: 1-Bromopentane + LiCuBu₂ → Nonane + LiBr + CuBr (b) Use lithium di-sec-propylcopper (LiCu(i-Pr)₂) as the Gilman reagent: 1-Bromopentane + LiCu(i-Pr)₂ → 3-Methyloctane + LiBr + CuBr (c) Use lithium di-tert-butylcopper (LiCu(t-Bu)₂) as the Gilman reagent: 1-Bromopentane + LiCu(t-Bu)₂ → 2,2-Dimethylheptane + LiBr + CuBr (d) Use lithium diethylcopper (LiCuEt₂) as the Gilman reagent and generate cis-2-butenyllithium first: 1-Bromopentane + LiCuEt₂ → 1-Heptene + LiBr + CuBr (e) Use lithium divinylcopper (LiCu(C₂H₃)₂) as the Gilman reagent: 1-Bromopentane + LiCu(C₂H₃)₂ → 1-Octene + LiBr + CuBr

Step-by-step solution

Identify the Gilman reagent

To transform 1-bromoentane into nonane, we need to couple with a four-carbon alkyl group. The appropriate Gilman reagent is therefore lithium di-n-butyylcopper (LiCuBu₂).

Write the equation

The equation for the synthesis of nonane using a Gilman reagent is as follows: 1-Bromopentane + LiCuBu₂ → Nonane + LiBr + CuBr #a) 3-Methyloctane#

Identify the Gilman reagent

To transform 1-bromopentane into 3-methyloctane, we need to couple with a three-carbon alkyl group that has a methyl branch. The appropriate Gilman reagent is lithium di-sec-propylcopper (LiCu(i-Pr)₂).

Write the equation

The equation for the synthesis of 3-methyloctane using a Gilman reagent is as follows: 1-Bromopentane + LiCu(i-Pr)₂ → 3-Methyloctane + LiBr + CuBr #c) 2,2-Dimethylheptane#

Identify the Gilman reagent

To transform 1-bromopentane into 2,2-dimethylheptane, we need to couple with a tert-butyl group. The appropriate Gilman reagent is lithium di-tert-butylcopper (LiCu(t-Bu)₂).

Write the equation

The equation for the synthesis of 2,2-dimethylheptane using a Gilman reagent is as follows: 1-Bromopentane + LiCu(t-Bu)₂ →2,2-Dimethylheptane + LiBr + CuBr #d) 1-Heptene#

Identify the Gilman reagent

To transform 1-bromopentane into 1-heptene, we need to couple with an ethyl group but generate cis-2-butenyllithium first. The appropriate Gilman reagent is lithium diethylcopper (LiCuEt₂).

Write the equation

The equation for the synthesis of 1-heptene using a Gilman reagent is as follows: 1-Bromopentane + LiCuEt₂ → 1-Heptene + LiBr + CuBr #e) 1-Octene#

Identify the Gilman reagent

To transform 1-bromopentane into 1-octene, we need to couple with a vinyl group (C₂H₃). The appropriate Gilman reagent is lithium divinylcopper (LiCu(C₂H₃)₂).

Write the equation

The equation for the synthesis of 1-octene using a Gilman reagent is as follows: 1-Bromopentane + LiCu(C₂H₃)₂ →1-Octene + LiBr + CuBr