Question

Show how to prepare each compound from the given starting compound through the use of a lithium diorganocopper (Gilman) reagent. (a) 4-Methylcyclopentene from 4 -bromocyclopentene (b) ( \(Z)\)-2-Undecene from \((Z)\)-1-bromopropene (c) 1-Butylcyclohexene from 1-iodocyclohexene (d) 1-Decene from 1-iodooctane (e) 1,8 -Nonadiene from 1,5 -dibromopentane

Short answer

Question: Show how to prepare each compound from the given starting compound using a lithium diorganocopper (Gilman) reagent. (a) 4-Methylcyclopentene from 4-bromocyclopentene (b) (Z)-2-Undecene from (Z)-1-bromopropene (c) 1-Butylcyclohexene from 1-iodocyclohexene (d) 1-Decene from 1-iodooctane (e) 1,8-Nonadiene from 1,5-dibromopentane Answer: (a) Use MeLiCu as the Gilman reagent: 4-bromocyclopentene + MeLiCu → 4-Methylcyclopentene (b) Use (Oct)2CuLi as the Gilman reagent: (Z)-1-bromopropene + (Oct)2CuLi → (Z)-2-Undecene (c) Use (Bu)2CuLi as the Gilman reagent: 1-iodocyclohexene + (Bu)2CuLi → 1-Butylcyclohexene (d) Use CH2=CH-CuLi as the Gilman reagent: 1-iodooctane + CH2=CH-CuLi → 1-Decene (e) Use CH2=CH-CH2-CuLi (2 equivalents) as the Gilman reagent: 1,5-dibromopentane + 2 CH2=CH-CH2-CuLi → 1,8-Nonadiene

Step-by-step solution

(a) 4-Methylcyclopentene from 4 -bromocyclopentene

To obtain 4-Methylcyclopentene from 4-bromocyclopentene, we will perform a nucleophilic substitution reaction using a Gilman reagent. First, identify the appropriate Gilman reagent: in this case, it will be \(\text{MeLiCu}\). The reaction will proceed as follows: 1. 4-bromocyclopentene + \(\text{MeLiCu}\) \(\rightarrow\) 4-Methylcyclopentene + \(\text{LiBrCu}\)

(b) (\( Z )\)-2-Undecene from \((Z)\)-1-bromopropene

To obtain (\( Z )\)-2-Undecene from \((Z)\)-1-bromopropene, we will perform a nucleophilic substitution reaction using a Gilman reagent. First, identify the appropriate Gilman reagent: in this case, it will be \(\text{(Oct)2CuLi}\). The reaction will proceed as follows: 1. \((Z)\)-1-bromopropene + \(\text{(Oct)2CuLi}\) \(\rightarrow\) (\( Z )\)-2-Undecene + \(\text{LiBrCu}\)

(c) 1-Butylcyclohexene from 1-iodocyclohexene

To obtain 1-Butylcyclohexene from 1-iodocyclohexene, we will perform a nucleophilic substitution reaction using a Gilman reagent. First, identify the appropriate Gilman reagent: in this case, it will be \(\text{(Bu)2CuLi}\). The reaction will proceed as follows: 1. 1-iodocyclohexene + \(\text{(Bu)2CuLi}\) \(\rightarrow\) 1-Butylcyclohexene + \(\text{LiICu}\)

(d) 1-Decene from 1-iodooctane

To obtain 1-Decene from 1-iodooctane, we will perform a nucleophilic substitution reaction using a Gilman reagent. First, identify the appropriate Gilman reagent: in this case, it will be \(\text{CH2=CH-CuLi}\). The reaction will proceed as follows: 1. 1-iodooctane + \(\text{CH2=CH-CuLi}\) \(\rightarrow\) 1-Decene + \(\text{LiICu}\)

(e) 1,8-Nonadiene from 1,5-dibromopentane

To obtain 1,8-Nonadiene from 1,5-dibromopentane, we will perform a nucleophilic substitution reaction using a Gilman reagent. First, identify the appropriate Gilman reagent (note that this requires two equivalent Gilman reagents): in this case, it will be \(\text{CH2=CH-CH2-CuLi}\). The reaction will proceed as follows: 1. 1,5-dibromopentane + 2 \(\text{CH2=CH-CH2-CuLi}\) \(\rightarrow\) 1,8-Nonadiene + \(\text{LiBrCu} + \text{LiBrCu}\)

Key concepts

Nucleophilic Substitution Reaction

In the realm of synthetic organic chemistry, one of the most fundamental and widely-applied reactions is the nucleophilic substitution reaction. It refers to a process where a nucleophile, which is a chemical species that is rich in electrons and seeks to share these electrons, displaces a leaving group attached to a carbon atom.

Imagine a molecule like a little fortress, with the carbon at the center surrounded by its army—the leaving group. The nucleophile, like a cunning invader, desires the valuable position the leaving group holds. When the nucleophile attacks, the leaving group is forced away, and the nucleophile takes its place, leading to the formation of a new molecule.

The allure of this type of reaction lies in its ability to create a vast array of complex molecules from simpler ones. In the case of using a lithium diorganocopper (Gilman) reagent, we look at an interesting variant of nucleophilic substitution where a carbon-copper bond acts as the nucleophile. This approach allows for the efficient and selective formation of new carbon-carbon bonds, opening up pathways to construct more complex organic structures, such as alkenes, cycloalkanes, and even more intricate architectural frameworks within organic molecules.

Synthetic Organic Chemistry

Diving deeper, synthetic organic chemistry is the science of constructing organic molecules through strategic chemical reactions. It’s akin to using building blocks to create complex structures, except in this scenario, we are dealing with atoms and molecules.

The beauty and challenge of synthetic chemistry lie in how these molecular blocks are cleverly put together. Making a new bond here, tweaking a functional group there; it’s all about manipulating those tiny bits and pieces on a molecular level.

With the Gilman reagent synthesis, as exemplified in the textbook exercise, we see how mastery in synthetic organic chemistry enables chemists to take a starting compound and, like an artist with a vision, transform it step by step into a new, desired compound. Reagents like the Gilman reagent serve as special tools that make certain chemical bonds more accessible, thus simplifying these complex transformations and expanding the chemist's capabilities to build a wide variety of molecules for pharmaceuticals, materials, and many other applications.

Alkene Synthesis

Alkenes, characterized by their carbon-carbon double bonds, are fundamental structures in organic chemistry and serve as precursors to a multitude of other organic compounds. But how do chemists make them? Well, alkene synthesis is one important chapter in the vast novel of organic synthesis.

One traditional method to create alkenes is by eliminating groups from a molecule, like pulling away a block from a Jenga tower to make it lean a certain way. However, the Gilman reagent provides an alternative route through the aforementioned nucleophilic substitution reaction.

Why is this significant?

The utilitarian aspect comes from the fact that this method facilitates the creation of alkenes with remarkable precision regarding where the double bond is placed and what groups are attached to the double-bonded carbons.

In the context of our exercise, we can see practical examples of converting halogenated compounds into alkenes by applying the Gilman reagent. This method is particularly precious in preparing alkenes with specific configurations, such as the (Z)-2-Undecene. The creation of such targeted molecules is invaluable in research and industry, where the exact structure of a molecule can dramatically influence its properties and efficacy.