Categories: C=C Bond Formation >
Synthesis of allenes
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Recent Literature
Various propargylic amines underwent a palladium-catalyzed hydrogen-transfer
reaction in the presence of (C6F5)3P,
giving the corresponding allenes in good yields.
H. Nakamura, T. Kamakura, M. Ishikura, J.-F. Biellmann, J. Am. Chem. Soc.,
2004, 126, 5958-5959.
Benzyl propargyl ethers react with a gold(I) catalyst to furnish substituted
allenes via a 1,5-hydride shift/fragmentation sequence. This transformation is
rapid and practical and can be performed under very mild conditions using
terminal as well as substituted alkyne substrates bearing a primary, secondary,
or tertiary benzyl ether group.
B. Bolte, Y. Odabachian, F. Gagosz, J. Am. Chem. Soc., 2010,
132, 7294-7296.
B. Bolte, Y. Odabachian, F. Gagosz, J. Am. Chem. Soc., 2010,
132, 7294-7296.
A metal-free, one-pot synthesis of substituted allenes from enones via the
corresponding α,β-unsaturated tosylhydrazones proceeds readily with high
compatibility of sensitive functional groups using a tertiary amine as a base.
This synthetic protocol provides synthetically important allenes without the use
of metallic reagents or catalysts.
M. Tang, C.-A. Fan, F.-M. Zhang, Y.-Q. Tu, W.-X. Zhang, A.-X. Wang, Org. Lett., 2008,
10, 5585-5588.
A copper hydride-catalyzed SN2′-reduction of propargylic carbonates
provides functionalized allenes in good yields. The method takes advantage of
the stabilizing effect of NHC ligands on CuH and offers high reactivity,
stereoselectivity, and functional group tolerance.
C. Deutsch, B. H. Lipshutz, N. Krause, Org. Lett., 2009,
11, 5010-5012.
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.
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.
A chemoselective isomerization of secondary-type propargylic alcohols under
Appel-type reaction conditions in the presence of Ph3P, CBr4
and additives gives allenic bromides, propargylic bromides and brominated
dienes.
N. Sakai, T. Maruyama, T. Konakahara, Synlett, 2009,
2105-2106.
A Rh-catalyzed coupling reaction between propargylic carbonates and a
silylboronate affords allenylsilanes in high yields. The reaction tolerates
various functional groups and proceeds with excellent chirality transfer.
H. Ohmiya, H. Ito, M. Sawamura, Org. Lett., 2009,
11, 5618-5620.
The Au-catalyzed hydrative rearrangement of 1,1-diethynylcarbinol acetates in
wet CH2Cl2 produces either
5-acetoxy-2-alkyl-2-cyclopentenones or acetoxymethyl α-alkylallenones as a major
product depending on the temperature, reaction time, and catalyst loading.
C. H. Oh, S. Karmakar, J. Org. Chem., 2009,
74, 370-374.
A Cu(O-t-Bu)-Xantphos catalyst system was effective for the preparation
of various allenylboronates with different substitution patterns, those with
functional groups, and an axially chiral one. A Lewis acid promoted
stereoselective addition of allenylboronates to aldehydes leads to
homopropargylic alcohols.
H. Ito, Y. Sasaki, M. Sawamura, J. Am. Chem. Soc., 2008,
130, 15774-15775.
A new, efficient method based on a palladium(0)-catalyzed reaction of
propargylic derivatives with various phosphorus nucleophiles produces
allenylphosphonates and their analogues with defined stereochemistry in the
allenic and the phosphonate moiety.
M. Kalek, T. Johansson, M. Jezowska, J. Stawinski, Org. Lett., 2010,
12, 4702-4704.
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.
