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Radical Substitution: Allylic Chlorination

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Typically, when alkenes react with halogens at low temperatures, an addition reaction occurs. However, upon increasing the temperature or under reaction conditions that form radicals, providing a low but steady concentration of halogen radicals, allylic substitution reaction is favored. This is because allylic hydrogens are very reactive as the formed intermediate is resonance stabilized. For example, when propene is treated with chlorine in the gas phase at 400 °C, it undergoes allylic...

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In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...

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Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
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Friedel–Crafts reactions were developed in 1877 by the French chemist Charles Friedel and the American chemist James Crafts. Friedel–Crafts alkylation refers to the replacement of an aromatic proton with an alkyl group via electrophilic aromatic substitution. A Lewis acid catalyst such as aluminum chloride reacts with an alkyl halide to form a carbocation. The resulting carbocation then reacts with the aromatic ring and undergoes a series of electron rearrangements before giving the final...

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Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

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Palladium-catalyzed allylic C-H fluorination.

Marie-Gabrielle Braun¹, Abigail G Doyle

¹Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.

Journal of the American Chemical Society

|August 17, 2013

Summary

This summary is machine-generated.

This study introduces the first catalytic allylic C-H fluorination using nucleophilic fluoride. The novel palladium/chromium cocatalyst system efficiently produces allylic fluorides with excellent regioselectivity under mild conditions.

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Area of Science:

Organic Chemistry
Organometallic Chemistry
Fluorination Chemistry

Background:

Allylic fluorides are valuable synthetic intermediates.
Existing methods for allylic fluorination often require prefunctionalized substrates or harsh conditions.
Development of direct C-H functionalization methods is a key goal in synthetic chemistry.

Purpose of the Study:

To report the first catalytic direct allylic C-H fluorination reaction.
To develop a method utilizing a nucleophilic fluoride source.
To establish a mild and regioselective protocol for synthesizing allylic fluorides.

Main Methods:

Utilized a palladium (Pd) and chromium (Cr) cocatalyst system.
Employed triethylamine trihydrofluoride (Et3N·3HF) as the nucleophilic fluoride source.
Investigated the reaction with simple olefin substrates.

Main Results:

Achieved the first catalytic direct allylic C-H fluorination with a nucleophilic fluoride.
Obtained good yields of allylic fluorides.
Demonstrated high branched-to-linear regioselectivity in the fluorination products.
Reaction proceeds under mild conditions.

Conclusions:

The developed Pd/Cr catalyzed reaction offers a powerful new route to allylic fluorides.
This method provides an alternative to traditional approaches requiring prefunctionalized starting materials.
The broad scope and mild conditions enhance its utility in organic synthesis.