Organozinc chemistry

Organozinc chemistry is the study of organometallic compounds that contain a carbon-zinc bond. These compounds are important in organic synthesis due to their reactivity and ability to form carbon-carbon bonds. Organozinc compounds are typically less reactive than other organometallics, such as organolithium or Grignard reagents, making them useful for selective transformations.

History

The first organozinc compound, diethylzinc, was discovered by Edward Frankland in 1849. This discovery marked the beginning of organometallic chemistry as a distinct field. Organozinc compounds have since been used in a variety of synthetic applications, including the Reformatsky reaction and Negishi coupling.

Synthesis

Organozinc compounds can be synthesized through several methods:

Direct Insertion

Direct insertion of zinc into organic halides

Direct insertion involves the reaction of zinc metal with organic halides to form organozinc compounds. This method is straightforward but often requires activation of the zinc surface.

Transmetallation

Transmetallation process

Transmetallation involves the exchange of organic groups between a metal and zinc. This method is commonly used to prepare organozinc reagents from organolithium or Grignard reagents.

Functional Group Exchange

Functional group exchange in organozinc chemistry

Functional group exchange allows for the conversion of one organozinc compound into another by exchanging the organic group attached to zinc.

Reactivity

Organozinc compounds are known for their mild reactivity, which allows for selective transformations in the presence of sensitive functional groups.

Carbon-Carbon Bond Formation

Zinc-mediated coupling reaction

Organozinc reagents are used in carbon-carbon bond-forming reactions, such as the Negishi coupling, where they react with organic halides in the presence of a palladium catalyst.

Carbonyl Additions

Addition of diphenylzinc to carbonyl compounds

Organozinc compounds can add to carbonyl groups to form alcohols. This reaction is less reactive than similar reactions with Grignard reagents, allowing for greater control.

Applications

Organozinc chemistry is widely used in the synthesis of complex organic molecules, including natural products and pharmaceuticals.

Reformatsky Reaction

Reformatsky reaction mechanism

The Reformatsky reaction involves the reaction of α-halo esters with aldehydes or ketones in the presence of zinc to form β-hydroxy esters.

Total Synthesis

Total synthesis using organozinc chemistry

Organozinc reagents are employed in the total synthesis of complex molecules, where their selectivity and mild reactivity are advantageous.

Related Pages

• Organometallic chemistry
• Grignard reagent
• Negishi coupling
• Reformatsky reaction