Editing Allenes (section)

==Synthesis==
Although allenes often require specialized syntheses, the parent allene, [[propadiene]] is produced industrially on a large scale as an equilibrium mixture with [[methylacetylene|propyne]]:
:<chem>H2C=C=CH2 <=> H3C-C#CH</chem>
This mixture, known as [[MAPP gas]], is commercially available.  At 298 K, the Δ''G°'' of this reaction is –1.9 kcal/mol, corresponding to ''K''<sub>eq</sub> = 24.7.<ref>{{Cite journal|last1=Robinson|first1=Marin S.|last2=Polak|first2=Mark L.|last3=Bierbaum|first3=Veronica M.|last4=DePuy|first4=Charles H.|last5=Lineberger|first5=W. C.|date=1995-06-01|title=Experimental Studies of Allene, Methylacetylene, and the Propargyl Radical: Bond Dissociation Energies, Gas-Phase Acidities, and Ion-Molecule Chemistry|url=https://doi.org/10.1021/ja00130a017|journal=Journal of the American Chemical Society|volume=117|issue=25|pages=6766–6778|doi=10.1021/ja00130a017|issn=0002-7863}}</ref>

The first allene to be synthesized was [[penta-2,3-dienedioic acid]], which was prepared by Burton and Pechmann in 1887. However, the structure was only correctly identified in 1954.<ref>{{Cite journal|last1=Jones|first1=E. R. H.|last2=Mansfield|first2=G. H.|last3=Whiting|first3=M. C.|date=1954-01-01|title=Researches on acetylenic compounds. Part XLVII. The prototropic rearrangements of some acetylenic dicarboxylic acids|url=https://pubs.rsc.org/en/content/articlelanding/1954/jr/jr9540003208|journal=Journal of the Chemical Society (Resumed)|language=en|pages=3208–3212|doi=10.1039/JR9540003208|issn=0368-1769}}</ref>

Laboratory methods for the formation of allenes include:
*from geminal dihalocyclopropanes and organolithium compounds (or metallic sodium or magnesium) in the [[Skattebøl rearrangement]] ([[Doering–LaFlamme allene synthesis]]) via rearrangement of cyclopropylidene carbenes/carbenoids
*from reaction of certain terminal [[alkyne]]s with [[formaldehyde]], [[copper(I) bromide]], and added base ([[Crabbé–Ma allene synthesis]])<ref>{{OrgSynth|title=One-Step Homologation of Acetylenes to Allenes: 4-Hydroxynona-1,2-diene [1,2-Nonadien-4-ol]|last1=Crabbé|first1=Pierre|last2=Nassim|first2=Bahman|last3=Robert-Lopes|first3=Maria-Teresa|collvol=7|collvolpages=276|volume=63|page=203|date=1985|prep=CV7P0276|doi=10.15227/orgsyn.063.0203}}</ref><ref>{{OrgSynth|title=Buta-2,3-dien-1-ol|first1=Hongwen|last1=Luo|first2=Dengke|last2=Ma|first3=Shengming|last3=Ma|year=2017|vol=94|page=153–166|prep=v94p0153|doi=10.15227/orgsyn.094.0153}}</ref>
*from propargylic halides by S<sub>N</sub>2′ displacement by an organocuprate<ref>{{Cite journal|last1=Yoshikai|first1=Naohiko|last2=Nakamura|first2=Eiichi|date=2012-04-11|title=Mechanisms of Nucleophilic Organocopper(I) Reactions|url=https://pubs.acs.org/doi/10.1021/cr200241f|journal=Chemical Reviews|language=en|volume=112|issue=4|pages=2339–2372|doi=10.1021/cr200241f|pmid=22111574|issn=0009-2665}}</ref>
*from [[dehydrohalogenation]] of certain [[halide|dihalides]]<ref>{{OrgSynth|title=Allene|last1=Cripps|first1=H. N.|last2=Kiefer|first2=E. F.|collvol=5|collvolpages=22|volume=42|page=12|date=1962|prep=CV5P0022|doi=10.15227/orgsyn.042.0012}}</ref>
*from reaction of a triphenylphosphinyl ester with an acid halide, a [[Wittig reaction]] accompanied by dehydrohalogenation<ref>{{cite journal|last1=Lang|first1=Robert W.|last2=Hansen|first2=Hans-Jürgen|title=Eine einfache Allencarbonsäureester-Synthese mittels der Wittig-Reaktion|trans-title=A simple synthesis of allene carboxylic acid esters by means of the Wittig reaction|journal=[[Helv. Chim. Acta]]|volume=63|issue=2|pages=438–455|date=1980|doi=10.1002/hlca.19800630215}}</ref><ref>{{OrgSynth|title=α-Allenic Esters from α-Phosphoranylidene Esters and Acid Chlorides: Ethyl 2,3-Pentadienoate [2,3-Pentadienoic acid, ethyl ester]|last1=Lang|first1=Robert W.|last2=Hansen|first2=Hans-Jürgen|collvol=7|collvolpages=232|volume=62|page=202|date=1984|prep=CV7P0232|doi=10.15227/orgsyn.062.0202}}</ref>
*from propargylic alcohols via the [[Myers allene synthesis]] protocol—a [[stereospecific]] process
*from metalation of allene or substituted allenes with BuLi and reaction with electrophiles (RX, R<sub>3</sub>SiX, D<sub>2</sub>O, etc.)<ref>{{Cite journal|last1=Michelot|first1=Didier|last2=Clinet|first2=Jean-Claude|last3=Linstrumelle|first3=Gérard|date=1982-01-01|title=Allenyllithium Reagents (VI)1. A Highly Regioselective Metalation of Allenic Hydrocarbons2. A Route to Mono, DI, TRI or Tetrasubstituted Allenes|url=https://doi.org/10.1080/00397918208061912|journal=Synthetic Communications|volume=12|issue=10|pages=739–747|doi=10.1080/00397918208061912|issn=0039-7911}}</ref>
The chemistry of allenes has been reviewed in a number of books<ref name=":0" /><ref>{{Cite book|url=https://www.worldcat.org/oclc/501315951|title=The chemistry of ketenes, allenes and related compounds. Part 1|series=PATAI'S Chemistry of Functional Groups|date=1980|publisher=Wiley|editor-last=Patai|editor-first=Saul|isbn=978-0-470-77160-0|location=Chichester|oclc=501315951}}</ref><ref>{{Cite book|url=https://www.worldcat.org/oclc/520990503|title=The chemistry of ketenes, allenes and related compounds. Part 2|series=PATAI'S Chemistry of Functional Groups|date=1980|publisher=Wiley|editor-last=Patai|editor-first=Saul|isbn=978-0-470-77161-7|location=Chichester|oclc=520990503}}</ref><ref name=":10">{{Cite book|last1=Brandsma|first1=L.|last2=Verkruijsse|first2=H.D.|url=https://www.worldcat.org/oclc/162570992|title=Synthesis of acetylenes, allenes and cumulenes : methods and techniques|date=2004|publisher=Elsevier|isbn=978-0-12-125751-4|edition=1st|location=Amsterdam|oclc=162570992}}</ref> and journal articles.<ref name=":2" /><ref name=":7">{{Cite journal|last=Pasto|first=Daniel J.|date=January 1984|title=Recent developments in allene chemistry|url=https://linkinghub.elsevier.com/retrieve/pii/S004040200191289X|journal=Tetrahedron|language=en|volume=40|issue=15|pages=2805–2827|doi=10.1016/S0040-4020(01)91289-X}}</ref><ref>{{Cite journal|last1=Zimmer|first1=Reinhold|last2=Dinesh|first2=Chimmanamada U.|last3=Nandanan|first3=Erathodiyil|last4=Khan|first4=Faiz Ahmed|date=2000-08-01|title=Palladium-Catalyzed Reactions of Allenes|url=https://pubs.acs.org/doi/10.1021/cr9902796|journal=Chemical Reviews|language=en|volume=100|issue=8|pages=3067–3126|doi=10.1021/cr9902796|pmid=11749314|issn=0009-2665}}</ref><ref name=":8">{{Cite journal|last=Ma|first=Shengming|date=2009-10-20|title=Electrophilic Addition and Cyclization Reactions of Allenes|url=https://pubs.acs.org/doi/10.1021/ar900153r|journal=Accounts of Chemical Research|language=en|volume=42|issue=10|pages=1679–1688|doi=10.1021/ar900153r|pmid=19603781|issn=0001-4842}}</ref><ref>{{Cite journal|last1=Alcaide|first1=Benito|last2=Almendros|first2=Pedro|last3=Aragoncillo|first3=Cristina|date=2010|title=Exploiting [2+2] cycloaddition chemistry: achievements with allenes|url=http://xlink.rsc.org/?DOI=B913749A|journal=Chem. Soc. Rev.|language=en|volume=39|issue=2|pages=783–816|doi=10.1039/B913749A|pmid=20111793|hdl=10261/29537 |issn=0306-0012|hdl-access=free}}</ref><ref>{{Cite journal|last=Pinho e Melo|first=Teresa M. V. D.|date=July 2011|title=Allenes as building blocks in heterocyclic chemistry|url=http://link.springer.com/10.1007/s00706-011-0505-7|journal=Monatshefte für Chemie - Chemical Monthly|language=en|volume=142|issue=7|pages=681–697|doi=10.1007/s00706-011-0505-7|s2cid=189843060|issn=0026-9247}}</ref><ref>{{Cite journal|last1=López|first1=Fernando|last2=Mascareñas|first2=José Luis|date=2011-01-10|title=Allenes as Three-Carbon Units in Catalytic Cycloadditions: New Opportunities with Transition-Metal Catalysts|url=https://onlinelibrary.wiley.com/doi/10.1002/chem.201002366|journal=Chemistry – A European Journal|language=en|volume=17|issue=2|pages=418–428|doi=10.1002/chem.201002366|pmid=21207554|issn=0947-6539}}</ref><ref>{{Cite journal|last1=Aubert|first1=Corinne|author2-link=Louis Fensterbank|last2=Fensterbank|first2=Louis|last3=Garcia|first3=Pierre|last4=Malacria|first4=Max|last5=Simonneau|first5=Antoine|date=2011-03-09|title=Transition Metal Catalyzed Cycloisomerizations of 1, n -Allenynes and -Allenenes|url=https://pubs.acs.org/doi/10.1021/cr100376w|journal=Chemical Reviews|language=en|volume=111|issue=3|pages=1954–1993|doi=10.1021/cr100376w|pmid=21391568|issn=0009-2665}}</ref><ref>{{Cite journal|last1=Krause|first1=Norbert|last2=Winter|first2=Christian|date=2011-03-09|title=Gold-Catalyzed Nucleophilic Cyclization of Functionalized Allenes: A Powerful Access to Carbo- and Heterocycles|url=https://pubs.acs.org/doi/10.1021/cr1004088|journal=Chemical Reviews|language=en|volume=111|issue=3|pages=1994–2009|doi=10.1021/cr1004088|pmid=21314182|issn=0009-2665}}</ref> Some key approaches towards allenes are outlined in the following scheme:<ref name=":3">{{Cite journal|last=Sydnes|first=Leiv K.|date=2003-04-01|title=Allenes from Cyclopropanes and Their Use in Organic SynthesisRecent Developments|url=https://pubs.acs.org/doi/10.1021/cr010025w|journal=Chemical Reviews|language=en|volume=103|issue=4|pages=1133–1150|doi=10.1021/cr010025w|pmid=12683779|issn=0009-2665}}</ref><ref name=":4">{{Cite journal|last1=Brummond|first1=Kay|author-link=Kay Brummond|last2=DeForrest|first2=Jolie|date=March 2007|title=Synthesizing Allenes Today (1982-2006)|url=http://www.thieme-connect.de/DOI/DOI?10.1055/s-2007-965963|journal=Synthesis|language=en|volume=2007|issue=6|pages=795–818|doi=10.1055/s-2007-965963|issn=0039-7881}}</ref><ref name=":5">{{Cite journal|last1=Yu|first1=Shichao|last2=Ma|first2=Shengming|date=2011|title=How easy are the syntheses of allenes?|url=http://xlink.rsc.org/?DOI=C0CC05640E|journal=Chemical Communications|language=en|volume=47|issue=19|pages=5384–5418|doi=10.1039/C0CC05640E|pmid=21409186|issn=1359-7345}}</ref><ref name=":6">{{Cite journal|last1=Tejedor|first1=David|last2=Méndez-Abt|first2=Gabriela|last3=Cotos|first3=Leandro|last4=García-Tellado|first4=Fernando|date=2013|title=Propargyl Claisen rearrangement: allene synthesis and beyond|url=http://xlink.rsc.org/?DOI=C2CS35311C|journal=Chem. Soc. Rev.|language=en|volume=42|issue=2|pages=458–471|doi=10.1039/C2CS35311C|pmid=23034723|hdl=10261/132538 |issn=0306-0012|hdl-access=free}}</ref>

[[File:Overview_common_allene_syntheses_Zhurakovskyi.svg]]

One of the older methods is the Skattebøl rearrangement<ref name=":3" /><ref>{{Cite journal|last1=Skattebøl|first1=Lars|last2=Nilsson|first2=Martin|last3=Lindberg|first3=Bengt|last4=McKay|first4=James|last5=Munch-Petersen|first5=Jon|date=1963|title=The Synthesis of Allenes from 1,1-Dihalocyclopropane Derivatives and Alkyllithium.|journal=Acta Chemica Scandinavica|language=en|volume=17|pages=1683–1693|doi=10.3891/acta.chem.scand.17-1683|issn=0904-213X|doi-access=free}}</ref><ref>{{Cite journal|last1=Moore|first1=William R.|last2=Ward|first2=Harold R.|date=December 1962|title=The Formation of Allenes from gem-Dihalocyclopropanes by Reaction with Alkyllithium Reagents 1,2|url=https://pubs.acs.org/doi/abs/10.1021/jo01059a013|journal=The Journal of Organic Chemistry|language=en|volume=27|issue=12|pages=4179–4181|doi=10.1021/jo01059a013|issn=0022-3263}}</ref> (also called the Doering–Moore–Skattebøl or Doering–LaFlamme<ref>{{Cite journal|last=Fedoryński|first=Michał|date=2003-04-01|title=Syntheses of gem -Dihalocyclopropanes and Their Use in Organic Synthesis|url=https://pubs.acs.org/doi/10.1021/cr0100087|journal=Chemical Reviews|language=en|volume=103|issue=4|pages=1099–1132|doi=10.1021/cr0100087|pmid=12683778|issn=0009-2665}}</ref><ref>{{Cite book|last1=Kurti|first1=Laszlo|last2=Czako|first2=Barbara|url=https://www.worldcat.org/oclc/850164343|title=Strategic Applications of Named Reactions in Organic Synthesis : Background and Detailed Mechanisms.|date=2005|publisher=Elsevier Science|isbn=978-0-08-057541-4|location=Burlington|pages=758|oclc=850164343}}</ref> rearrangement), in which a gem-dihalocyclopropane '''3''' is treated with an organolithium compound (or dissolving metal) and the presumed intermediate rearranges into an allene either directly or via carbene-like species. Notably, even strained allenes can be generated by this procedure.<ref>{{Cite journal|last1=Shi|first1=Min|last2=Shao|first2=Li-Xiong|last3=Lu|first3=Jian-Mei|last4=Wei|first4=Yin|last5=Mizuno|first5=Kazuhiko|last6=Maeda|first6=Hajime|date=2010-10-13|title=Chemistry of Vinylidenecyclopropanes|url=https://pubs.acs.org/doi/10.1021/cr900381k|journal=Chemical Reviews|language=en|volume=110|issue=10|pages=5883–5913|doi=10.1021/cr900381k|pmid=20518460|issn=0009-2665}}</ref> Modifications involving leaving groups of different nature are also known.<ref name=":3" /> Arguably, the most convenient modern method of allene synthesis is by [[sigmatropic rearrangement]] of [[Propargyl group|propargylic substrates]].<ref name=":4" /><ref name=":5" /><ref name=":6" /> Johnson–Claisen<ref name=":6" /> and Ireland–Claisen<ref>{{Cite journal|last1=Ireland|first1=Robert E.|last2=Mueller|first2=Richard H.|last3=Willard|first3=Alvin K.|date=May 1976|title=The ester enolate Claisen rearrangement. Stereochemical control through stereoselective enolate formation|url=https://pubs.acs.org/doi/abs/10.1021/ja00426a033|journal=Journal of the American Chemical Society|language=en|volume=98|issue=10|pages=2868–2877|doi=10.1021/ja00426a033|issn=0002-7863}}</ref> rearrangements of ketene acetals '''4''' have been used a number of times to prepare allenic esters and acids. Reactions of vinyl ethers '''5''' (the Saucy–Marbet rearrangement) give allene aldehydes,<ref>{{Cite journal|last1=Kurtz|first1=Kimberly C.M.|last2=Frederick|first2=Michael O.|last3=Lambeth|first3=Robert H.|last4=Mulder|first4=Jason A.|last5=Tracey|first5=Michael R.|last6=Hsung|first6=Richard P.|date=April 2006|title=Synthesis of chiral allenes from ynamides through a highly stereoselective Saucy–Marbet rearrangement|url=https://linkinghub.elsevier.com/retrieve/pii/S0040402006001268|journal=Tetrahedron|language=en|volume=62|issue=16|pages=3928–3938|doi=10.1016/j.tet.2005.11.087}}</ref> while propargylic sulfenates '''6''' give allene sulfoxides.<ref>{{Cite journal|last1=Mukai|first1=Chisato|last2=Kobayashi|first2=Minoru|last3=Kubota|first3=Shoko|last4=Takahashi|first4=Yukie|last5=Kitagaki|first5=Shinji|date=March 2004|title=Construction of Azacycles Based on Endo-Mode Cyclization of Allenes|url=https://pubs.acs.org/doi/10.1021/jo035729f|journal=The Journal of Organic Chemistry|language=en|volume=69|issue=6|pages=2128–2136|doi=10.1021/jo035729f|pmid=15058962|issn=0022-3263}}</ref><ref>{{Cite journal|last1=Mukai|first1=Chisato|last2=Ohta|first2=Masaru|last3=Yamashita|first3=Haruhisa|last4=Kitagaki|first4=Shinji|date=October 2004|title=Base-Catalyzed Endo-Mode Cyclization of Allenes: Easy Preparation of Five- to Nine-Membered Oxacycles|url=https://pubs.acs.org/doi/10.1021/jo0488614|journal=The Journal of Organic Chemistry|language=en|volume=69|issue=20|pages=6867–6873|doi=10.1021/jo0488614|pmid=15387613|issn=0022-3263}}</ref> Allenes can also be prepared by [[nucleophilic substitution]] in '''9''' and '''10''' (nucleophile Nu<sup>−</sup> can be a hydride anion), [[1,2-elimination]] from '''8''', proton transfer in '''7''', and other, less general, methods.<ref name=":4" /><ref name=":5" />