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Synthesis of substituted allenes

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Cross-coupling of propargylic bromide with Grignard reagent enables a convenient method for the synthesis of terminal allenes. The reaction of propargylic bromide with 1.2 equivalents of Grignard reagent catalyzed by a complex of Ni(acac)2  and Ph3P in THF produces terminal allenes in good yields and high regioselectivities at room temperature.
Q. Li, H. Gau, Synlett, 2012, 23, 747-750.


A simple copper-catalyzed enantioselective synthesis of axially chiral chloroallenes from the propargylic dichlorides leads to exclusive formation of the desired allenes with good enantioselectivities. Further transformations to trisubstituted allenes or terminal alkynes with a propargylic quaternary carbon center keep a high level of enantiopurity.
H. Li, D. Müller, L. Guénée, A. Alexakis, Org. Lett., 2012, 14, 5880-5883.


The palladium-catalyzed of triorganoindium reagents to propargylic esters afforded via an SN2' rearrangement allenes in good yields and with high regioselectivity. The reaction of chiral, nonracemic propargylic esters takes place with high anti-stereoselectivity providing allenes with high enantiomeric excess.
R. Riveiros, D. Rodríguez, J. P. Sestelo, L. A. Sarandeses, Org. Lett., 2006, 8, 1403-1406.


Copper-catalyzed γ-selective coupling between propargylic phosphates and alkylboron compounds affords multisubstituted allenes with various functional groups. The reaction of enantioenriched propargylic phosphates to give axially chiral allenes proceeds with excellent chirality transfer with 1,3-anti stereochemistry.
H. Ohmiya, U. Yokobori, Y. Makida, M. Sawmura, Org. Lett., 2011, 13, 6312-6315.


Copper-catalyzed alkylation and arylation of chiral propargylic phosphates using alkyl boranes and arylboronic esters as organoboron nucleophiles enables the asymmetric synthesis of trisubstituted allenes with excellent chirality transfer and regioselectivity, together with good functional group compatibility.
M. R. Uehling, S. T. Marionni, G. Lalic, Org. Lett., 2012, 14, 362-365.


The SN2′ reaction of propragyl mesylates with organozinc reagents was dramatically improved in DMSO as solvent, and the conversion of a chiral substrate was successfully achieved without loss of optical purity using a LiCl-free diorganozinc reagent.
K. Kobayashi, H. Naka, A. E. H. Wheatley, Y. Kondo, Org. Lett., 2008, 10, 3375-3377.


The β-alkoxide elimination reaction of aryl- or alkyl-subsituted propargylic ethers with Negishi reagent leads to allenes after hydrolysis, whereas TMS-substituted substrates afford alkynes. Subsequent coupling reactions of the zirconium intermediates with aryl iodides in the presence of Pd(PPh3)4/CuCl provide a straightforward route for the synthesis of multisubstituted allenes.
H. Zhang, X. Fu, J. Chen, E. Wang, Y. Liu, X. Li, J. Org. Chem., 2009, 74, 9351-9358.


An efficient synthetic method provides tri- and tetra-substituted allenes by the reaction of allylindium reagents with 3°-propargyl alcohols. Allylindium reagents are generated in situ from indium and allyl bromides.
K. Lee, P. H. Lee, Org. Lett., 2008, 10, 2441-2444.


Sulfonate-bearing chiral bidentate N-heterocyclic carbene (NHC) complexes of copper enable catalytic enantioselective allylic substitutions of allylic phosphonates with commercially available allenylboronic acid that result in addition of an allenyl group and formation of tertiary or quaternary C-C bonds in up to 95% yield, >98% SN2′ selectivity, and 98% ee.
B. Jung, A. H. Hoveyda, J. Am. Chem. Soc., 2012, 134, 1490-1493.


Lithiation of 1-aryl-3-alkylpropadienes and subsequent transmetalation with zinc bromide followed by Pd-catalyzed Negishi coupling reactions with halides afforded the corresponding trisubstituted allenes in a highly regioselective fashion with good yields. A plausible regioselective lithiation mechanism was proposed on the basis of deuterium labeling experiments.
J. Zhao, Y. Liu, S. Ma, Org. Lett., 2008, 10, 1521-1523.


1,1-diarylpropadienes and 1,3-diarylpropynes can be prepared by the sequential lithiation of 1-aryl-1-propynes, transmetalation, and the corresponding Pd(0)-catalyzed cross-coupling with aryl halides.
S. Ma, Q. He, X. Zhang, J. Org. Chem., 2005, 70, 3336-3338.


Tertiary homopropargyl alcohols can be used as allenylmetal equivalents in a palladium-catalyzed reaction with aryl halides to provide arylallenes regioselectively. The reaction includes retro-propargylation, which proceeds in a concerted fashion via a cyclic transition state and transfers the stereochemistry of homopropargyl alcohols through C-C bond cleavage.
S. Hayashi, K. Hirano, H. Yorimitsu, K. Oshima, J. Am. Chem. Soc., 2008, 130, 5048-5049.


Pd-catalyzed cross-coupling reactions of electron-rich and electron-poor aryl iodides with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield.
P. H. Lee, J. Mo, D. Kang, D. Eom, C. Park, C.-H. Lee, Y M. Jung, H. Hwang, J. Org. Chem., 2011, 76, 312-315.


Pd(0)-catalyzed carbonylation of (Z)-2-en-4-yn carbonates in the presence of CO and an alcohol gives vinylallenyl esters with an exclusively E-configuration in high yields. The unreactivity of E-configured enyne carbonates may indicate that the reaction is promoted via the cooperative coordination of palladium with both alkynyl and carbonate moieties.
G. E. Akpınar, M. Kuş, M. Uçncu, E. Karakuş, L. Artok, Org. Lett., 2011, 13, 748-751.


Addition of α-alkenylzirconacyclopentenes to aldehyde enables a highly stereoselective synthesis of β-hydroxyallenes with multiple stereogenic centers including allenic axial chirality, as well as center chirality. Remarkably, the reaction occurs with completely different chemoselectivity in comparison with the usual alkyl- or aryl-substituted zirconacyclopentenes.
Y. Zhou, J. Chen, C. Zhao, E. Wang, Y. Liu, Y. Li, J. Org. Chem., 2009, 74, 5326-5330.


Reactions of various carbonyl compounds with organoindium reagent in situ generated from indium and 1-bromopent-4-en-2-yne derivatives gives  functionalized vinyl allenols in good yields. Treatment of vinyl allenols with gold catalyst, dienophile, or indium trihalide produced functionalized dihydrofuran, cyclohexene, or 2-halo-1,3-diene derivatives in very good yields.
J. Park, S. Hong, P. H. Lee, Org. Lett., 2008, 10, 5067-5070.


A AuCl-catalyzed, flexible synthesis of highly substituted, benzyl-protected phenols unites enal/enones and benzyl allenyl ethers in a [3+3] fashion in two steps, allowing excellent control of substitution at the benzene ring.
X. Huang, L. Zhang, Org. Lett., 2007, 9, 4627-4630.


Arynes, generated in situ from ortho-silylaryl triflates, undergo ene reaction with alkynes possessing propargylic hydrogen in the presence of KF/18-crown-6 in THF at room temperature to give substituted phenylallenes in good to moderate yields.
T. T. Jayanth, M. Jeganmohan, M.-J. Cheng, S.-Y. Chu, C.-H. Cheng, J. Am. Chem. Soc., 2006, 128, 2232-2233.


Various arylallenes and alkenylallenes were prepared via coupling of allenylstannanes with aryl iodides or alkenyl iodides in the presence of Pd(PPh3)4 as catalyst, LiCl, and DMF as solvent.
C.-W. Huang, M. Shanmugasundaram, H.-M. Chang, C.-H. Cheng, Tetrahedron, 2003, 59, 3635-3641.


Enantioenriched propargyl mesylates or perfluorobenzoates react with α-(N-carbamoyl)alkylcuprates to afford scalemic α-(N-carbamoyl) allenes. Subsequent N-Boc deprotection and AgNO3-promoted cyclization afford enantioenriched N-alkyl-3-pyrrolines.
R. K. Dieter, N. Chen, V. K. Gore, J. Org. Chem., 2006, 71, 8755-8760.


Homoallenic alcohols are prepared from various propargyl vinyl ethers using a trinuclear gold(I)-oxo complex, [(Ph3PAu)3O]BF4, as a catalyst for propargyl Claisen rearrangement at room temperature.
B. D. Sherry, F. D. Toste, J. Am. Chem. Soc., 2004, 126, 15978-15979.


Various arylallenes and alkenylallenes were prepared via coupling of allenylstannanes with aryl iodides or alkenyl iodides in the presence of Pd(PPh3)4 as catalyst, LiCl, and DMF as solvent.
C.-W. Huang, M. Shanmugasundaram, H.-M. Chang, C.-H. Cheng, Tetrahedron, 2003, 59, 3635-3641.