Categories: C=C Bond Formation >
Synthesis of allenes
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.
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.
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.