Why does lithiation of arylethers result in a selective ortho product?

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In summary, the conversation discusses the use of butyl litium as a reagent to deprotanate the ring of anisole, with the understanding that the resulting lithium will bond with the ring. The question then arises about the purpose of this reaction and whether it can be done without the OMe group, as well as the potential analogy between a lithiated ring and a negatively charged carbon. Further research reveals that the RLi reagent is highly selective for the ortho product and may not follow a typical electrophilic aromatic substitution mechanism. The conversation ends with a recommendation to read a specific article for more information on the topic.
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Inertia
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Is it possible someone can explain the point of doing this, I am having a really hard time grasping the concept. For example if I have anisole and I use butyl litium as a reagent, my understanding is that it will behave like a base and deprotanate the ring, resulting in a lithium bonded to the ring. Since OMe is an activating group it is para/meta directing. One might expect the lithium to therefore go to the para position, but I think I am right in saying it goes to the meta position due to a stabilised transition state where the Li coordinates with the oxygen.

I am not sure what the point of doing this is, what is to be done with the lithiated anisole? Can the reaction be done without OMe, will any EWG do, or indeed could it be done with plain benzene? And what is the point of lithiating? Do we treat a lithiated ring as being analogous to a negative charge stuck on a carbon and it can therefore behave like a nucleophile?

Rings are nucleophilic anyway so what is the point?
 
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  • #2
This was an interesting question that I wanted to know about also so I did a quick literature scan. Apparently the RLi reagent is very selective for the ortho product. This reaction may not proceed through a typical electrophilic aromatic substitution type of mechanism. You can read a bit about it here: J. Org. Chem. 1997, 62, 3024-3025. It is a short communication and very accessible, in my opinion. The author makes some statements about potential complication with the ether moiety being responsible for the predominant ortho product. Unfortunately I've about used up my free time, so you're on your own from here.
 

1. What is the purpose of lithiation of arylethers in scientific research?

The purpose of lithiation of arylethers is to introduce a lithium atom into the aryl ring, which allows for further functionalization and modification of the molecule. This process is often used in organic synthesis to create new compounds for various applications.

2. How is lithiation of arylethers typically carried out in the laboratory?

Lithiation of arylethers can be carried out using various methods, including direct metalation with a lithium reagent or indirect metalation through a palladium-catalyzed reaction. The choice of method depends on the specific arylether and desired functional group to be introduced.

3. What are some common applications of lithiation of arylethers?

Lithiation of arylethers is commonly used in the synthesis of pharmaceuticals, agrochemicals, and other organic compounds. It can also be used to prepare building blocks for materials science and to study the reactivity of aryl compounds.

4. Are there any limitations or challenges associated with lithiation of arylethers?

One limitation of lithiation of arylethers is that it can be difficult to control the regioselectivity of the reaction, meaning that multiple isomers may be produced. Additionally, some arylethers may be unreactive towards lithiation, requiring the use of more reactive metalating agents.

5. How does lithiation of arylethers contribute to the overall understanding of organic chemistry?

Lithiation of arylethers allows for the creation of new and complex molecules, which can help expand our understanding of the reactivity and properties of organic compounds. It also provides a valuable tool for the synthesis of compounds with specific functional groups that may have practical applications in various fields.

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