WordNet

of or pertaining to the allyl radical
(genetics) either of a pair (or series) of alternative forms of a gene that can occupy the same locus on a particular chromosome and that control the same character; "some alleles are dominant over others" (同)allelomorph
the univalent unsaturated organic radical C3H5; derived from propylene (同)allyl_group, allyl radical

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/05/07 17:20:45」(JST)

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Structure of the allyl group.

resonance structure of the allyl anion

An allyl group is a substituent with the structural formula H₂C=CH-CH₂R, where R is the connection to the rest of the molecule. It is made up of a methylene (-CH₂-), attached to a vinyl group (-CH=CH₂). The name is derived from the Latin word for garlic, Allium sativum. Theodor Wertheim isolated an allyl derivative from garlic oil and named it Schwefelallyl.^[1] The term allyl applies to many compounds related to H₂C=CH-CH₂, which includes thousands of different chemical compounds, some of which are of practical or everyday importance.

Nomenclature and bonding

Allyl is a widely used term in organic chemistry.^[2] The unpaired electron is delocalized. Allylic radicals, anions, and cations are often discussed as intermediates in reactions. All feature three contiguous sp²-hybridized carbon centers.

MO diagram for pi-orbitals on allyl. The middle MO labeled Ψ₂ is singly occupied in the allyl radical. In the allyl cation Ψ₂ is unoccupied and in the allyl anion it is doubly occupied. Hydrogen atoms are omitted from this picture.

Allylic sites

A site on the saturated carbon atom is called the "allylic position" or "allylic site." A group attached at this site is sometimes described as "allylic." Thus, CH₂=CHCH₂OH "has an allylic hydroxyl group." Allylic C-H bonds are about 15% weaker than the C-H bonds in ordinary sp³ carbon centers and are thus more reactive. As one practical consequence of this heightened reactivity, the production of acrylonitrile exploits the easy oxidation of the allylic C-H centers in propene. Benzylic and allylic are related in terms of structure, bond strength, and reactivity. Other reactions that tend to occur with allylic compounds are allylic oxidations, ene reactions, and the Tsuji–Trost reaction. Benzylic groups are related to allyl groups; both show enhanced reactivity.

Pentadienyl

A CH₂ group connected to two vinyl groups is said to be doubly allylic. The bond dissociation energy of C-H bonds on a doubly allylic centre is about 10% less than the bond dissociation energy of a C-H bond that is allylic. The weakened C-H bonds reflect the high stability of the resulting "pentadienyl" radicals. Compounds containing the C=C-CH₂-C=C linkages, e.g. linoleic acid derivatives, are prone to autoxidation, which can lead to polymerization or form semisolids. This reactivity pattern is fundamentally related to the film-forming behavior of the "drying oils" which are components of oil paints and varnishes.

Homoallylic

The term homoallylic refers to the position on a carbon skeleton next to an allylic position. In CH₂=CHCH₂CH₂Cl, the chloride occupies a homoallylic position.

The allylic, homoallylic and doubly allylic sites are highlighted in red.

Allyl compounds

Many substituents can be attached to the allyl group to give stable compounds. Allyl alcohol has the structure H₂C=CH-CH₂OH. It contains two sp²-hybridized carbon centers and one sp³-hybridized carbon center. Another example of a simple allyl compound is allyl chloride. Substituted versions of the parent allyl group, such as the trans-but-2-en-1-yl or crotyl group (CH₃CH=CH-CH₂-), may also be referred to as allylic groups. Many allylic compounds are lachrymatory.

Allyl ligands in organometallic chemistry

The allyl ligand is commonly encountered in organometallic chemistry. Most commonly, allyl ligands bind to metals via all three carbon centers, the so-called η³-binding mode. η¹-allyl complexes are also known. The most popular allyl reagent is probably allyl palladium chloride. They are usually generated by oxidative addition of allylic halides. This route affords pi-allyl nickel compounds, such as (allyl)₂Ni₂Cl₂:^[3]

2 Ni(CO)₄ + 2 ClCH₂CH=CH₂ → Ni₂(μ-Cl)₂(η³-C₃H₅)₂ + 8 CO

Also in organometallic chemistry nucleophilic addition to allyl ligands can occur.

References

^ Wertheim, Theodor (1844). "Untersuchung des Knoblauchöls". Annalen der Chemie und Pharmacie 51 (3): 289. doi:10.1002/jlac.18440510302.
^ March, J. “Advanced Organic Chemistry” $th Ed. J. Wiley and Sons, 1992: New York. ISBN 0-471-60180-2.
^ Martin F. Semmelhack and Paul M. Helquist (1988), "Reaction of Aryl Halides with π-Allylnickel Halides: Methallylbenzene", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6p0722 ; Coll. Vol. 6: 722

English Journal

Catalytic decarboxylative alkylation of β-keto acids with sulfonamides via the cleavage of carbon-nitrogen and carbon-carbon bonds.

Yang CF, Wang JY, Tian SK.SourceJoint Laboratory of Green Synthetic Chemistry, Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China. tiansk@ustc.edu.cn.
Chemical communications (Cambridge, England).Chem Commun (Camb).2011 Aug 7;47(29):8343-5. Epub 2011 Jun 22.
An efficient decarboxylative alkylation reaction of β-keto acids with N-benzylic or N-allylic sulfonamides has been developed, for the first time, through sequential cleavage of carbon-nitrogen and carbon-carbon bonds in the presence of 10 mol% of FeCl(3).
PMID 21695345

Direct substitution of the hydroxy group with highly functionalized nitrogen nucleophiles catalyzed by Au(iii).

Ohshima T, Nakahara Y, Ipposhi J, Miyamoto Y, Mashima K.SourceGraduate School of Pharmaceutical Sciences, Kyushu University and CREST, JST, Fukuoka, Japan. ohshima@phar.kyushu-u.ac.jp.
Chemical communications (Cambridge, England).Chem Commun (Camb).2011 Aug 7;47(29):8322-4. Epub 2011 Jun 21.
A direct catalytic substitution of various allylic and benzylic alcohols with synthetically useful, but acid-sensitive Boc, Bus, and Dios protected amine nucleophiles, which have not been well utilized for Lewis acid catalysis, with various functionalities (OTBS, OTHP, etc.) was efficiently catalyze
PMID 21695315

Japanese Journal

Nucleophilic allylation of N,O-acetals with allylic alcohols promoted by Pd/Et3B and Pd/Et2Zn systems

Yamaguchi Yumi,Hashimoto Mariko,Tohyama Katsumi,Kimura Masanari
Tetrahedron Letters 52(8), 913-915, 2011-02-23
… Pd/Et3B and Pd/Et2Zn systems promote the nucleophilic allylations of 2-aminotetrahydrofuran and 2-aminotetrahydropyran with allylic alcohols to provide ω-hydroxyhomoallylamines in high yields. …
NAID 120002949360