関: allenic

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/04/24 16:35:17」(JST)

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Propadiene, the simplest allene, is also known as allene.

An allene is a compound in which one carbon atom has double bonds with each of its two adjacent carbon centres. Allenes are classified as polyenes with cumulated dienes. The parent compound of allene is propadiene. Compounds with an allene-type structure but with more than three carbon atoms are called cumulenes. Allenes are much more reactive than most other alkenes. For example, their reactivity with gaseous chlorine is more like the reactivity of alkynes than that of alkenes.

Structure and bonding

Geometry

3D view of propadiene (allene).

The central carbon of allene forms two sigma bonds and two pi bonds. The central carbon is sp-hybridized, and the two terminal carbons are sp²-hybridized. The bond angle formed by the three carbons is 180°, indicating linear geometry for the carbons of allene. It can also be viewed as an "extended tetrahedral" with a similar shape to methane.

Symmetry

The symmetry and isomerism of allenes has long fascinated organic chemists.^[1] For allenes with four identical substituents, there exist two twofold axes of rotation through the center carbon, inclined at 45° to the CH₂ planes at either end of the molecule. The molecule can thus be thought of as a two-bladed propeller. A third twofold axis of rotation passes through the C=C=C bonds, and there is a mirror plane passing through both CH₂ planes. Thus this class of molecules belong to the D_2d point group. Because of the symmetry, an unsubstituted allene has no net dipole moment.

R and S configurations are determined by precedences of the groups attached to the axial section of the molecule when viewed along that axis. The front plane is given higher priority over the other and the final assignment is given from priority 2 to 3 (i.e. the relationship between the two planes).

An allene with two different substituents on each of the two carbons will be chiral because there will no longer be any mirror planes. Where A has a greater priority than B according to the Cahn-Ingold-Prelog priority rule, the configuration of the axial chirality can be determined by considering the substituents on the front atom followed by the back atom when viewed along the allene axis. For the bottom, only the group of higher priority need be considered. Chiral allenes have been recently used as building blocks in the construction of organic materials with exceptional chiroptical properties.^[2]

Synthesis

Although allenes often require specialized syntheses, the parent, propadiene is produced on a large scale as an equilibrium mixture with methylacetylene:

H₂C=C=CH₂ ⇌ CH₃C≡CH

This mixture, known as MAPP gas, is commercially available.

Laboratory methods for the formation of allenes include:

from geminal dihalocyclopropanes and organolithium compounds in the Skattebøl rearrangement.
from reaction of certain terminal alkynes with formaldehyde, copper(I) bromide and added base^[3]
from dehydrohalogenation of certain dihalides.^[4]
from reaction of a triphenylphosphinyl ester with an acid halide, a Wittig reaction accompanied by dehydrohalogenation^[5]

References

^ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7
^ Angew Chem Int Ed Engl. 2012 Mar 19;51(12):2818-28. doi: 10.1002/anie.201108001
^ Organic Syntheses, Coll. Vol. 7, p.276 (1990); Vol. 63, p.203 (1985). Link
^ Organic Syntheses, Coll. Vol. 5, p.22 (1973); Vol. 42, p.12 (1962) Link
^ Helv. Chim. Acta, 63, 438 (1980); Org. Synth. Coll., 7, 232 (1990)
^ Bhagwat; Devaprabhakara (1972). "Selective hydrogenation of allenes with chlorotris-(triphenylphosphine) rhodium catalyst". Tetrahedron Lett. 13 (15): 1391. doi:10.1016/S0040-4039(01)84636-0.

External links

Stereochemistry study guide
Synthesis of allenes

English Journal

Stereospecific biosynthesis of (9S,13S)-10-oxo-phytoenoic acid in young maize roots.

Ogorodnikova AV1, Gorina SS1, Mukhtarova LS1, Mukhitova FK1, Toporkova YY1, Hamberg M2, Grechkin AN3.
Biochimica et biophysica acta.Biochim Biophys Acta.2015 Sep;1851(9):1262-70. doi: 10.1016/j.bbalip.2015.05.004. Epub 2015 May 22.
Profiling of oxylipins from young maize roots revealed complex patterns of products mainly originating from the combined actions of 9- and 13-lipoxygenases and allene oxide synthase (AOS). A distinctive feature was the high content of the cyclopentenone 10-oxo-11-phytoenoic acid (10-oxo-PEA). Incuba
PMID 26008579

A Striking Case of Enantioinversion in Gold Catalysis and Its Probable Origins.

Ilg MK1, Wolf LM1, Mantilli L1, Farès C1, Thiel W1, Fürstner A2.
Chemistry (Weinheim an der Bergstrasse, Germany).Chemistry.2015 Aug 24;21(35):12279-84. doi: 10.1002/chem.201502160. Epub 2015 Jul 23.
The cyclization of the hydroxy-allene 2 to the tetrahydrofuran 3 catalyzed by the gold-phosphoramidite complex 1, after ionization with an appropriate silver salt AgX, is one of the most striking cases of enantioinversion known to date. The major reason why the sense of induction can be switched fro
PMID 26211656

Insights into the Gold-Catalyzed Propargyl Ester Rearrangement/Tandem Cyclization Sequence: Radical versus Gold Catalysis-Myers-Saito- versus Schmittel-Type Cyclization.

Rettenmeier E1, Hansmann MM1, Ahrens A1, Rübenacker K1, Saboo T1, Massholder J1, Meier C1, Rudolph M1, Rominger F1, Hashmi AS2,3.
Chemistry (Weinheim an der Bergstrasse, Germany).Chemistry.2015 Aug 20. doi: 10.1002/chem.201501725. [Epub ahead of print]
A detailed study of the gold-catalyzed tandem 1,3-carboxy migration/allene-enyne cycloisomerization was undertaken. It was found that after the initial allene formation the selectivity of the reaction is strongly influenced by the polarization of the remaining alkyne. Depending on the substitution p
PMID 26291466

Japanese Journal

アレンおよびジエン誘導体のリビング配位重合と精密反応性・機能性高分子への応用 (特集高分子合成の新潮流(2))

日本接着学会誌 = Journal of the Adhesion Society of Japan : adhesion 53(5), 149-156, 2017
NAID 40021217820

Creation of Novel Cyclization Methods Using <i>sp</i>-Hybridized Carbon Units and Syntheses of Bioactive Compounds

ＣＨＥＭＩＣＡＬ　＆　ＰＨＡＲＭＡＣＥＵＴＩＣＡＬ　ＢＵＬＬＥＴＩＮ 65(6), 511-523, 2017
NAID 130005686029

Rh[Ⅰ]-Catalyzed Cycloaddition between Allenyl π-Bonds and C-C Triple Bonds

有機合成化学協会誌 74(11), 1108-1118, 2016
NAID 130005433323

「allenic」

　　[★]

アレンの

関: allene

「allene oxide synthase」

　　[★]

アレンオキシド合成酵素

関: AOS

[1] Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7

[2] Angew Chem Int Ed Engl. 2012 Mar 19;51(12):2818-28. doi: 10.1002/anie.201108001

[3] Organic Syntheses, Coll. Vol. 7, p.276 (1990); Vol. 63, p.203 (1985). Link

[4] Organic Syntheses, Coll. Vol. 5, p.22 (1973); Vol. 42, p.12 (1962) Link

[5] Helv. Chim. Acta, 63, 438 (1980); Org. Synth. Coll., 7, 232 (1990)

[6] Bhagwat; Devaprabhakara (1972). "Selective hydrogenation of allenes with chlorotris-(triphenylphosphine) rhodium catalyst". Tetrahedron Lett. 13 (15): 1391. doi:10.1016/S0040-4039(01)84636-0.

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allene