Organocopper reagents are powerful tools in organic synthesis, offering unique reactivity and selectivity. These compounds excel at forming , particularly in conjugate additions and . Their ability to control stereochemistry makes them valuable in complex molecule synthesis.
Understanding the different types of organocopper reagents, such as Gilman and , is crucial for synthetic planning. These compounds' structure, bonding, and preparation methods influence their reactivity. Mastering organocopper chemistry opens up new possibilities in organic synthesis and catalysis.
Types of organocopper reagents
Organocopper reagents play a crucial role in organic synthesis due to their unique reactivity and selectivity
These reagents allow for precise control in carbon-carbon bond formation and functional group transformations
Understanding different types of organocopper compounds enhances synthetic planning and execution in complex molecule synthesis
Gilman reagents
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Organocopper cross-coupling reaction for C–C bond formation on highly sterically hindered ... View original
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Organocopper cross-coupling reaction for C–C bond formation on highly sterically hindered ... View original
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Re-orienting coupling of organocuprates with propargyl electrophiles from S N 2′ to S N 2 with ... View original
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Organocopper cross-coupling reaction for C–C bond formation on highly sterically hindered ... View original
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Re-orienting coupling of organocuprates with propargyl electrophiles from S N 2′ to S N 2 with ... View original
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Consist of dialkylcuprates with the general formula R2CuLi
Prepared by reacting organolithium compounds with copper(I) salts in a 2:1 ratio
Exhibit enhanced reactivity and selectivity compared to simple organolithium reagents
Commonly used in and cross-coupling processes
Examples include dimethylcuprate (Me2CuLi) and diphenylcuprate (Ph2CuLi)
Normant cuprates
Higher-order cuprates with the general formula R2Cu(CN)Li2
Formed by reacting organolithium compounds with copper(I) cyanide
Demonstrate increased thermal stability and reactivity compared to
Particularly effective in SN2' reactions and conjugate additions to α,β-unsaturated carbonyl compounds
Examples include lithium dimethylcyanocuprate and lithium dibutylcyanocuprate
Heterocuprates
Contain two different organic groups attached to copper
Prepared by sequential addition of different organolithium reagents to copper salts
Allow for selective transfer of one organic group while the other acts as a non-transferable ligand
Useful in chemoselective transformations and asymmetric synthesis
Examples include RCu(2-thienyl)CNLi2 and PhCu(Me)Li
Structure and bonding
Organocopper compounds exhibit unique structural features due to copper's electronic configuration
Understanding these structural aspects is crucial for predicting reactivity and designing effective synthetic strategies
The bonding in organocopper reagents influences their stability, reactivity, and selectivity in organic transformations
Copper oxidation states
Copper primarily exists in +1 oxidation state in organocopper reagents
Cu(I) forms linear or trigonal planar complexes due to its d10 electronic configuration
Copper's ability to access multiple oxidation states (+1, +2, +3) enables various reaction mechanisms
Cu(I) compounds are typically colorless or pale yellow, while Cu(II) compounds are often blue or green
Redox processes involving Cu(I)/Cu(III) are important in many organocopper-mediated reactions
Ligand effects
Nature of ligands significantly influences the reactivity and selectivity of organocopper reagents
Electron-donating ligands increase electron density on copper, enhancing nucleophilicity
π-acceptor ligands (phosphines) can stabilize reactive intermediates and modulate reactivity
Chiral ligands enable asymmetric transformations by creating a chiral environment around copper
Examples of common ligands include alkyl groups, cyanide, phosphines, and N-heterocyclic carbenes
Aggregation in solution
Organocopper compounds often form aggregates in solution, affecting their reactivity
Aggregation state depends on factors like solvent polarity, temperature, and concentration
Lower-order aggregates (dimers, trimers) are generally more reactive than higher-order structures
Polar solvents (THF, ether) tend to break up aggregates, increasing reactivity
Additives like TMEDA or HMPA can be used to control aggregation and enhance reactivity
Preparation methods
Synthesis of organocopper reagents requires careful control of reaction conditions
Various methods allow for the preparation of different types of organocopper compounds
Choice of preparation method depends on desired reactivity, stability, and functional group tolerance
From organolithium compounds
Most common method for preparing Gilman reagents and other organocopper compounds
Involves reacting organolithium reagents with copper(I) salts (CuI, CuBr, CuCN)
Typically performed at low temperatures (-78°C to 0°C) to control reactivity
Stoichiometry crucial for determining the type of organocopper reagent formed
Example: 2RLi+CuI→R2CuLi+LiI
From Grignard reagents
Alternative method using less reactive organometallic precursors
Grignard reagents (RMgX) react with copper(I) salts to form organocopper compounds
Generally requires higher temperatures compared to organolithium method
Useful when organolithium reagents are too reactive or unavailable
Example: 2RMgBr+CuI→R2CuMgBr+MgBrI
Direct copper insertion
Involves direct insertion of copper metal into organic halides
Useful for preparing functionalized organocopper reagents
Often requires activation of copper (copper powder, Rieke copper)
Tolerates many functional groups incompatible with organolithium or Grignard reagents
Example: RX+Cu0→RCuX
X = Br, I
Often performed in polar aprotic solvents (DMF, DMSO)
Reactivity and mechanisms
Organocopper reagents exhibit unique reactivity patterns distinct from other organometallics
Understanding reaction mechanisms is crucial for predicting outcomes and optimizing conditions
Reactivity can be fine-tuned by modifying the structure of the organocopper reagent
SN2' reactions
Organocopper reagents excel at SN2' (conjugate displacement) reactions
Involve nucleophilic attack at the γ-position of allylic substrates
Proceed with inversion of configuration at the γ-carbon
Mechanism involves initial π-complexation followed by oxidative addition and reductive elimination
Example: reaction of allyl acetate with dimethylcuprate to form 1-butene
Conjugate addition reactions
Hallmark reaction of organocopper reagents, especially with α,β-unsaturated carbonyl compounds
Proceed via initial coordination to the π-system followed by 1,4-addition
Highly chemoselective for 1,4-addition over 1,2-addition
Can be rendered enantioselective using chiral ligands or auxiliaries
Example: addition of methylcuprate to cyclohexenone to form 3-methylcyclohexanone
Cross-coupling reactions
Organocopper reagents participate in various cross-coupling reactions
Include Ullmann coupling, Castro-Stephens coupling, and copper-catalyzed azide-alkyne cycloaddition
Often involve Cu(I)/Cu(III) redox cycles
Mechanism typically includes oxidative addition, transmetalation, and reductive elimination steps
Example: Ullmann coupling of aryl halides to form biaryls
Synthetic applications
Organocopper reagents find widespread use in organic synthesis due to their unique reactivity
These compounds enable transformations that are difficult or impossible with other organometallics
Applications range from simple functional group interconversions to complex natural product synthesis
Carbon-carbon bond formation
Organocopper reagents excel at forming new carbon-carbon bonds
Particularly useful for adding alkyl, aryl, and vinyl groups to various substrates
Allow for selective functionalization of complex molecules
Enable construction of quaternary carbon centers
Examples include:
Conjugate addition to enones
Carbocupration of alkynes
Cross-coupling reactions to form biaryls
Stereochemistry control
Organocopper reagents often exhibit high levels of stereoselectivity
Enable stereospecific SN2' reactions with allylic substrates
Allow for diastereoselective conjugate additions to chiral enones
Can be used in combination with chiral ligands for enantioselective transformations
Examples include:
Asymmetric conjugate addition to form chiral β-substituted ketones
Stereospecific coupling of chiral alkylcopper reagents
Functional group transformations
Organocopper compounds facilitate various functional group interconversions
Allow for selective manipulations in the presence of sensitive functionalities
Enable chemoselective transformations difficult with other organometallics
Useful for late-stage functionalization of complex molecules
Examples include:
Conversion of to alkenes via β-elimination
Selective reduction of α,β-unsaturated carbonyl compounds
Electrochemical generation of organocopper reagents
Applications in total synthesis
Increasing use of organocopper chemistry in the synthesis of complex natural products
Exploitation of copper's unique reactivity for key bond-forming steps
Application of copper-catalyzed reactions for late-stage functionalization
Integration of organocopper methods in diversity-oriented synthesis
Examples include:
Use of copper-catalyzed azide-alkyne cycloaddition in the synthesis of bioactive peptides
Application of asymmetric copper-catalyzed conjugate addition in steroid synthesis
Key Terms to Review (20)
Aldehydes: Aldehydes are organic compounds containing a carbonyl group (C=O) where the carbon is bonded to at least one hydrogen atom, making them distinct from ketones. This unique structure allows aldehydes to participate in various chemical reactions, particularly those involving nucleophiles, making them important intermediates in organic synthesis and a key feature in many biochemical processes.
Alkyl halides: Alkyl halides are organic compounds containing a carbon chain bonded to a halogen atom (such as fluorine, chlorine, bromine, or iodine). These compounds are significant in organic synthesis as they can undergo various reactions, including substitution and elimination, making them versatile intermediates in the formation of more complex molecules.
Carbanion mechanism: A carbanion mechanism refers to a reaction pathway in which a carbanion, a negatively charged carbon species, acts as a nucleophile to initiate a reaction. In these mechanisms, the carbanion can attack electrophiles, leading to the formation of new carbon-carbon or carbon-heteroatom bonds. This type of mechanism is particularly relevant in the context of organocopper reagents, where the unique properties of carbanions facilitate various nucleophilic substitutions and additions.
Carbon-carbon bonds: Carbon-carbon bonds are the connections formed between carbon atoms, which are fundamental to organic molecules and play a crucial role in determining the structure and reactivity of organic compounds. These bonds can be single, double, or triple, affecting the geometry and physical properties of the molecules they comprise. Understanding these bonds is key for working with organocopper reagents, as they often participate in forming new carbon-carbon bonds during synthesis reactions.
Conjugate addition reactions: Conjugate addition reactions involve the addition of a nucleophile to the β-carbon of an α,β-unsaturated carbonyl compound. This type of reaction allows for the formation of new carbon-carbon bonds and is significant in organic synthesis, particularly when using organometallic reagents like organocopper reagents. The outcome of these reactions often leads to more complex molecules, enhancing synthetic pathways.
Electrophilicity: Electrophilicity refers to the ability of a chemical species to act as an electrophile, meaning it is attracted to electrons and can accept an electron pair from a nucleophile during a chemical reaction. This characteristic is crucial in organic reactions, as electrophiles are often key players in mechanisms such as nucleophilic acyl substitution, functional group transformations, and organocopper reactions. Understanding electrophilicity helps in predicting reaction pathways and the reactivity of various organic compounds.
Formation of carbon-carbon bonds: The formation of carbon-carbon bonds is a fundamental process in organic chemistry that involves the creation of connections between carbon atoms, which is essential for building complex organic molecules. This process allows for the construction of various structures, including alkanes, alkenes, alkynes, and aromatic compounds, facilitating the synthesis of a wide range of chemical entities. Efficient methods for creating these bonds are critical in both synthetic organic chemistry and the development of pharmaceuticals and materials.
Gilman Reagents: Gilman reagents, also known as organocuprates, are organometallic compounds that contain lithium or copper atoms bonded to carbon atoms. They are highly versatile in organic synthesis and are particularly useful for nucleophilic substitutions and additions to carbonyl compounds, allowing for the formation of carbon-carbon bonds.
Henry Gilman: Henry Gilman was a prominent chemist known for his contributions to organic chemistry, particularly in the development of methods for synthesizing carbon-carbon bonds and studying organocopper reagents. His work laid the foundation for key techniques in organic synthesis, influencing how enolates can be alkylated and enhancing our understanding of reaction mechanisms in forming complex molecules.
Heterocuprates: Heterocuprates are a class of organocopper reagents that feature two different types of metal centers, typically copper and another metal, which can facilitate unique reactivity patterns in organic synthesis. These reagents are particularly known for their ability to act as nucleophiles, allowing for the formation of carbon-carbon bonds through cross-coupling reactions with various electrophiles. The presence of the additional metal component can enhance the selectivity and efficiency of these reactions.
Metalation mechanism: The metalation mechanism is a process in which a metal reagent, often a transition metal or organometallic compound, interacts with an organic molecule to form a new metal-carbon bond. This mechanism is crucial for facilitating various transformations in organic synthesis, particularly when using organocopper reagents that can effectively insert into carbon-hydrogen bonds, creating a new reactive site for further reactions.
Normant cuprates: Normant cuprates are a class of organocopper reagents characterized by their stable, non-aggregated forms that are useful in various organic transformations. They are named after the chemist who first described their unique properties and reactivity. These reagents are particularly significant for their ability to undergo nucleophilic reactions, enabling the formation of carbon-carbon bonds in synthetic organic chemistry.
Organometallic character: Organometallic character refers to the unique properties and behaviors exhibited by compounds that contain a bond between a carbon atom and a metal atom. This characteristic plays a significant role in reactivity, where the carbon-metal bond can exhibit ionic, covalent, or polar-covalent properties depending on the metal's electronegativity and oxidation state, impacting the compound's ability to participate in various chemical reactions.
Pyrophoric Nature: Pyrophoric nature refers to the ability of a substance to spontaneously ignite upon exposure to air, typically due to its high reactivity with oxygen. This characteristic is crucial for certain organometallic compounds, including organocopper reagents, as it dictates how these compounds must be handled and stored to prevent accidents during their use in synthetic organic chemistry.
Richard R. Schrock: Richard R. Schrock is an American chemist known for his significant contributions to the field of organic chemistry, particularly in the development of metal-catalyzed reactions such as olefin metathesis. His work has greatly advanced the understanding and application of organocopper reagents, which are important tools in organic synthesis for forming carbon-carbon bonds.
Selectivity in nucleophilic attack: Selectivity in nucleophilic attack refers to the preference of a nucleophile to react with a specific electrophile or a specific site within a molecule over others. This concept is crucial in organic synthesis, where the outcomes of reactions depend heavily on the chosen nucleophile and the electrophilic centers present in substrates. Selectivity influences product formation, yielding desired compounds while minimizing side reactions and byproducts.
Sn2' reactions: sn2' reactions are a specific type of nucleophilic substitution reaction where a nucleophile attacks a carbon atom that is also undergoing a simultaneous rearrangement. This reaction often involves the migration of a neighboring group and typically occurs at tertiary or secondary carbons, where steric hindrance is a consideration. The dual process of substitution and rearrangement leads to unique reaction pathways, making it an important concept in understanding complex organic transformations.
Stability of Carbanions: The stability of carbanions refers to the relative tendency of these negatively charged carbon species to remain in their anionic form without undergoing protonation or other reactions. Factors such as electronegativity, hybridization, and resonance significantly affect carbanion stability, making it an essential concept in understanding reaction mechanisms involving nucleophiles and their behavior in various organic transformations.
Synthesis of alcohols: The synthesis of alcohols involves the creation of alcohol compounds, typically through various chemical reactions that introduce hydroxyl groups (-OH) into organic molecules. This process is essential in organic chemistry as alcohols serve as vital intermediates in the production of a wide range of chemicals, including pharmaceuticals, solvents, and fuels. Two notable methods to synthesize alcohols include using Grignard reagents and organocopper reagents, both of which play significant roles in forming new carbon-carbon bonds and facilitating alcohol formation.
Toxicity: Toxicity refers to the degree to which a substance can cause harm to living organisms. It encompasses various factors, including the type of chemical, the dose, the route of exposure, and the duration of exposure. Understanding toxicity is essential for assessing the safety of compounds used in chemical reactions, especially when dealing with organocopper reagents that can have harmful effects on human health and the environment.