Allylic Coupling
Allylic Coupling - Related Videos
06:46
Facile Preparation of (2Z,4E)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
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Cited by 1 •
2017
The ruthenium-catalyzed olefination of electron-deficient alkenes with allyl acetate is described here. By using aminocarbonyl as a directing group, this external oxidant-free protocol has high efficiency and good stereo- and regioselectivity, opening a novel synthetic route to (Z,E)-butadiene skeletons.
01:27
π Molecular Orbitals of the Allyl Radical
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2025
Allyl radicals are three-carbon conjugated systems. They are readily formed as intermediates in halogenation reactions of alkenes involving the addition of halogen to the allylic carbon instead of the double bond. As seen in allyl cations and anions, each of the three sp2-hybridized carbon atoms in allyl radicals has an unhybridized p orbital. These orbitals combine to give three π molecular orbitals. The allyl systems have identical molecular orbitals but differ in the number of π electrons.
01:31
Radical Substitution: Allylic Chlorination
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2023
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...
01:27
Radical Substitution: Allylic Bromination
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2025
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...
01:18
π Molecular Orbitals of the Allyl Cation and Anion
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2025
An allyl group is a three-carbon conjugated system where the sp³-hybridized allylic carbon is bonded to a CH=CH2 group via a single bond. Allyl anions can be obtained by treating propene with a strong base that can deprotonate methyl groups. Allyl cations are formed as intermediates during substitution reactions involving allylic halides. In both cases, the hybridization of the allylic carbon changes from sp3 to sp2, giving rise to a carbon chain with three sp2-hybridized carbons, each with an...
FAQs
The π-allyl metal intermediate serves as the reactive platform created when a palladium catalyst activates an allylic electrophile. A coupling partner or nucleophile then attacks this intermediate, forming a new bond while determining how the allylic framework is connected. This step is central to achieving useful regioselectivity and, in many cases, stereochemical control.
Regioselectivity determines which position of the allylic system forms the new bond, whereas stereochemistry describes the three-dimensional outcome of that connection. Controlling both features allows chemists to construct the intended substituted alkene rather than a mixture of possible products. This precision is especially valuable when assembling complex molecular structures for chemical and biological studies.
An organometallic reagent can provide a carbon-based partner, supporting carbon-carbon bond construction, while other nucleophiles can introduce heteroatoms and produce carbon-heteroatom bonds. Thus, the partner selected determines the broad bond type installed on the allylic framework. This flexibility helps adapt the reaction to different synthetic targets without changing its fundamental activation and attack sequence.
A typical sequence begins with an allylic electrophile and a palladium catalyst. Catalyst activation generates a π-allyl metal intermediate, after which an organometallic reagent or another nucleophile is introduced as the attacking partner. Bond formation at this stage produces the coupled product, with the reaction designed to favor the desired regioselective and stereochemical outcome.
Chemists may select this strategy when a target requires a substituted alkene together with a new carbon-carbon or carbon-heteroatom bond. Its ability to connect an activated allylic substrate with varied partners makes it useful in constructing pharmaceuticals, natural products, and other complex molecules. The method is particularly relevant when controlled bond placement is important to the target structure.
Current research focuses on catalysts that use less expensive elements, substrates that expand the range of compatible starting materials, and reaction designs that improve selective bond construction. These goals address both practical and synthetic limitations: lower catalyst cost can improve accessibility, broader compatibility can support more substrates, and greater selectivity can simplify preparation of complex molecular targets.