Organocuprates (Gilman Reagents)
TLDRProfessor Dave discusses organocuprates, a type of organometallic reagent used in organic synthesis. Prepared from organolithium reagents and copper bromide, organocuprates, also known as Gilman reagents, are less reactive than their lithium counterparts. They are primarily used for conjugate addition to alpha-beta unsaturated ketones, attaching alkyl groups at the beta position, which is a valuable technique in synthetic chemistry. Additionally, they can be used for simple SN2 reactions on alkyl halides, extending alkyl chains.
Takeaways
- π Organocuprates are organometallic reagents containing copper, prepared from organolithium reagents and copper bromide.
- π The preparation of organocuprates involves a process called transmetallation, where copper doesn't insert into the alkyl halide like lithium or magnesium would.
- π Organocuprates, also known as Gilman reagents, are represented with two 'CuLi' indicating copper as the central atom with a formal negative charge and two alkyl groups attached.
- π The most common application of organocuprates is in conjugate addition reactions, where they react with alpha-beta unsaturated ketones to form new compounds with the alpha-beta unsaturation removed.
- π Organocuprates are less reactive than organolithium compounds, making them 'softer' and more selective in their reactions.
- π― The conjugate addition involves the organocuprate attacking the beta position of the alpha-beta unsaturated ketone, facilitated by the negative charge on copper and resonance stabilization.
- π§ͺ Aqueous acidic workup after the reaction reforms the carbonyl group and leads to the formation of the final product, typically a ketone.
- π¬ The reaction mechanism involves the alkyl group (methanide) attacking the beta position, neutralizing the copper atom, and subsequent rearrangement of the pi bonds.
- π· The presence of resonance structures explains the electrophilic nature of the beta position, despite the overall negative charge on the organocuprate.
- βοΈ Organocuprates are useful in synthetic strategies for attaching large alkyl groups specifically at the beta position to a carbonyl group.
- π An alternate application of organocuprates includes SN2 reactions, where the alkyl group can displace a halogen to extend an alkyl chain.
Q & A
What are organocuprates and why are they considered organometallic reagents?
-Organocuprates are organic compounds that contain copper, which makes them organometallic reagents. They are similar to Grignard reagents and organolithium reagents, as they involve a metal-carbon bond.
How are organocuprates typically prepared?
-Organocuprates are usually prepared through a process called transmetallation, where two equivalents of an organolithium reagent react with copper bromide, resulting in a copper anion with two alkyl groups attached and a lithium bromide byproduct.
What is the significance of the lithium counter ion in organocuprates?
-The lithium counter ion in organocuprates serves as a positive counter ion to balance the formal negative charge on the copper anion, which bears the alkyl groups.
What is the main application of organocuprates in organic chemistry?
-The primary application of organocuprates is in conjugate addition reactions, where they can attach an alkyl group to the beta position of an alpha-beta unsaturated carbonyl compound.
Why do organocuprates preferentially attack the beta position in alpha-beta unsaturated ketones?
-Organocuprates attack the beta position because the negative charge on the copper anion can be neutralized when the carbonyl carbon leaves with both electrons, making the beta position electrophilic and favorable for attack.
How does the reaction of an organocuprate with an alpha-beta unsaturated ketone differ from the reaction of Grignard or organolithium reagents?
-Grignard and organolithium reagents typically attack the carbonyl carbon directly (1,2 addition), while organocuprates perform a 1,4 addition, attaching the alkyl group to the beta position instead.
What is the role of resonance in the electrophilicity of the beta position in the reaction with organocuprates?
-Resonance allows for the drawing of a contributing structure with a formal positive charge on the beta carbon, indicating electron deficiency and making it a site of electrophilic attack for the organocuprate.
What happens to the alpha-beta unsaturation after the reaction with an organocuprate?
-The alpha-beta unsaturation is lost after the reaction with an organocuprate, as the alkyl group is attached to the beta position, and the pi bond is broken.
Can organocuprates be used for simple SN2 reactions?
-Yes, organocuprates can also be used for simple SN2 reactions, where the alkyl group can displace a halogen in an alkyl halide to form a longer alkyl chain.
What is the synthetic utility of organocuprates in attaching large alkyl fragments to a molecule?
-Organocuprates are useful for attaching large alkyl fragments to a molecule at the beta position relative to a carbonyl group, providing a precise and reliable synthetic technique for such modifications.
How is the final product of a conjugate addition reaction with an organocuprate typically processed?
-The final product is typically processed with an aqueous acidic workup, which reforms the carbonyl group and protonates the alkoxide, leading to the formation of the desired ketone.
Outlines
π§ͺ Preparation and Properties of Organocuprates
Professor Dave introduces organocuprates, a type of organometallic reagent that involves copper and is derived from organolithium reagents. The preparation process involves a reaction between organolithium and copper bromide, resulting in a copper anion with alkyl groups attached and a lithium counter ion. Organocuprates, also known as Gilman reagents, differ from Grignard and organolithium reagents in their method of preparation, which is through a process called transmetallation. The summary explains the structural components of organocuprates and their unique role in chemical reactions due to the formal negative charge on copper and the presence of alkyl groups.
π Applications of Organocuprates in Organic Synthesis
This paragraph delves into the primary application of organocuprates, which is the conjugate addition to Ξ±,Ξ²-unsaturated ketones. Unlike Grignard or organolithium reagents that would add to the carbonyl carbon, organocuprates preferentially attack the Ξ²-carbon, leading to the formation of a new carbon-carbon bond and the neutralization of the copper anion. The summary highlights the mild reactivity of organocuprates compared to organolithium compounds and their utility in attaching alkyl groups to specific positions in molecules, particularly in the presence of Ξ±,Ξ²-unsaturation. It also briefly mentions an alternate application, the SN2 reaction, where organocuprates can be used to extend alkyl chains by displacing halogens in alkyl halides.
Mindmap
Keywords
π‘Organocuprates
π‘Organometallic
π‘Grignard Reagents
π‘Organolithium Reagents
π‘Transmetallation
π‘Copper Anion
π‘Lithium Counter Ion
π‘Conjugate Addition
π‘Alpha-Beta Unsaturated Ketone
π‘Michael Addition
π‘SN2 Reaction
Highlights
Organocuprates are organic compounds involving copper, classified as organometallic reagents.
They are prepared from organolithium reagents through a process called transmetallation.
Transmetallation is necessary because copper does not insert into alkyl halides like lithium and magnesium do.
Organocuprates, also known as Gilman reagents, have two alkyl groups attached to a copper anion with a lithium counter ion.
Organocuprates are less reactive than organolithium compounds, making them 'softer' reagents.
Their common application is in conjugate addition to alpha-beta unsaturated ketones.
Organocuprates attack the beta position of the alpha-beta unsaturated ketone, unlike Grignard or organolithium reagents.
The copper anion's negative charge is neutralized when the alkyl group attaches, making the reaction favorable.
Resonance structures explain the electron deficiency at the site of attack for organocuprates.
Aqueous acidic workup reforms the carbonyl group after the conjugate addition.
Organocuprates can be used for synthetic strategies to attach large portions of a molecule at the beta position to a carbonyl.
The 1,4 addition with organocuprates is a key technique for specific synthetic applications.
An alternate application of organocuprates includes simple SN2 reactions on alkyl halides.
Organocuprates are versatile for attaching alkyl groups, including long alkyl fragments, to specific molecular positions.
The primary purpose of using organocuprates is for the conjugate addition to carbonyl-containing compounds with alpha-beta unsaturation.
Understanding the reactivity and application of organocuprates is crucial for advanced organic synthesis techniques.
Transcripts
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