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Synthesis of allenes
A copper-catalyzed decarboxylative coupling reaction of aryl alkynyl carboxylic acid, paraformaldehyde, and dicyclohexylamine in diglyme at 100°C for 2 h provides terminal allenes in good yields. The method showed good functional group tolerance.
J. Lim, J. Choi, H.-S. Kim, I.S. Kim, K. C. Nam, J. Kim, S. Lee, J. Org. Chem., 2016, 81, 303-308.
Treatment of 1,1-dichloroalk-1-enes with Cp2Ti[P(OEt)3]2 produced organotitanium species, which reacted with aldehydes and ketones to afford allenes.
T. Shono, K. Ito, A. Tsubouchi, T. Takeda, Org. Biomol. Chem., 2005, 3, 2914-2916.
Lithium alkoxides of β-silylallylic alcohols underwent the Peterson elimination in DMF to give allenes. A one pot process for a Peterson allenation reaction of carbonyl compounds using (Z)-(1-lithio-1-alkenyl)trimethylsilanes is described.
A. Tsubouchi, T. Kira, T. Takeda, Synlett, 2006, 2577-2580.
Simple and mild indium- and zinc-mediated dehalogenation reactions of vicinal dihalides in an aqueous solvent enable the synthesis of various allenylmethyl aryl ethers and monosubstituted allenes in very good yields.
M.-H. Lin, W.-S. Tsai, L.-Z. Lin, S.-F. Hung, T.-H. Chuang, Y.-J. Su, J. Org. Chem., 2011, 76, 8518-8523.
A CuI-catalyzed synthesis of 1,3-disubstituted allenes from 1-alkynes by the reaction with various N-tosylhydrazones as readily available starting materials is operationally simple and gives the desired products in good yields. The reaction tolerates various functional groups.
M. L. Hossain, F. Ye, Y. Zhang, J. Wang, J. Org. Chem., 2013, 78, 1236-1241.
Terminal allenes can be synthesized in good yields using ethyne as coupling partner in a copper-mediated cross-coupling reaction with N-tosylhydrazones or α-diazoacetate. This coupling method offers excellent functional group tolerance. Copper carbene migratory insertion is proposed as the key step.
F. Ye, C. Wang, X. Ma, M. L. Hossain, Y. Xia, Y. Zhang, J. Wang, J. Org. Chem., 2015, 80, 647-652.
An efficient protocol for the palladium-catalyzed Heck alkynylation using XPhos as ligand and Cs2CO3 as the base, couples a wide range of functionalized terminal alkynes and substituted benzyl chlorides. An excess amount of base and higher reaction temperatures allows the synthesis of allenes in a one-pot procedure.
C. H. Larsen, K. W. Anderson, R. E. Tundel, S. L. Buchwald, Synlett, 2006, 2941-2946.
1,2,3,4-tetrahydroisoquinoline (THIQ) mediates a practical synthesis of 1,3-disubstituted allenes from terminal alkynes and aldehydes under mild conditions in the presence of CuBr first and then ZnI2. A wide range of aldehydes and terminal alkynes are tolerated, affording the allene products in good yield.
G.-J. Jiang, Q.-H. Zheng, M. Dou, L.-G. Zhou, W. Meng, Z.-X. Yu, J. Org. Chem., 2013, 78, 11783-11793.
ZnI2 is a catalyst for a one-step synthesis of allenes from terminal alkynes and both aromatic and aliphatic aldehydes with morpholine as the base in toluene. The reaction proceeds via propargylic amines, which were converted to allenes by a sequential hydride transfer and β-elimination process. Functionalities such as halide, hydroxyl, or amine are tolerated.
J. Kuang, S. Ma, J. Am. Chem. Soc., 2010, 132, 1786-1787.
The reaction of 1-alkynes with Cy2NH and paraformaldehyde mediated by CuI (0.5 equiv) in refluxing dioxane produces terminal allenes in much higher yields than previously reported protocols and many functional groups such as mesylate, hydroxyl group, ether, amide, etc. are tolerated.
J. Kuang, S. Ma, J. Org. Chem., 2009, 74, 1763-1765.
A robust synthesis of allenoates via a Pd-catalyzed β-hydride elimination of (E)-enol triflates offers low catalyst loadings, mild reaction conditions, and the ability to access all four patterns of substituted allenoates from a single substrate class.
M. El Arba, S. E. Dibrell, I. T. Crouch, D. E. Frantz, Org. Lett., 2017, 19, 5446-5449.
Enantiomerically enriched 2,3-allenols were prepared by the CuBr-mediated homologation of the relatively easily available optically active terminal propargylic alcohols with paraformaldehyde in the presence of diisopropylamine.
S. Ma, H. Hou, S. Zhao, G. Wang, Synthesis, 2002, 1643-1645.
A one-pot synthesis of allenes by the 2-nitrobenzenesulfonylhydrazide-mediated coupling of hydroxyaldehydes or ketones with alkynyl trifluoroborate salts involves in situ formation of a sulfonylhydrazone that reacts with alkynyl trifluoroborates to generate a transient propargylic hydrazide species. Decomposition of this unstable hydrazide via an intermediate monoalkyldiazine produces the allene products.
D. A. Mundal, K. E. Lutz, R. J. Thomson, J. Am. Chem. Soc., 2012, 134, 5782-5785.
An asymmetric boronate addition to sulfonyl hydrazones catalyzed by chiral biphenols provides enantioenriched allenes in a traceless Petasis reaction. The resulting Mannich product from nucleophilic addition eliminates sulfinic acid, yielding a propargylic diazene that performs an alkyne walk to afford the allene. Two enantioselective approaches have been developed for the synthesis of allylic hydroxyl allenes and 1,3-alkenyl allenes.
Y. Jiang, A. B. Diagne, R. J. Thomson, S. E. Schaus, J. Am. Chem. Soc., 2017, 139, 1826-1829.
CuBr and ZnI2 catalyze an efficient asymmetric synthesis of axially chiral allenols with up to 97% ee from readily available propargylic alcohols, aliphatic or aromatic aldehyde, pyrrolidine, and commerically available ligands. The alcohol unit in the terminal alkynes plays a very important role for ensuring high enantioselectivity via coordination.
J. Ye, S. Li, B. Chen, W. Fan, J. Kuang, J. Liu, Y. Liu, B. Miao, B. Wan, Y. Wang, X. Xie, Q. Yu, W. Yuan, S. Ma, Org. Lett., 2012, 14, 1346-1349.
A Cu-catalyzed coupling of α-substituted-α-diazoesters with terminal alkynes gives substituted allenoates. Key to the development of a selective method was the recognition that an adventitous base catalyzes the isomerization to form the allenoate product. A plausible mechanism is proposed, based in part on evidence against a mechanism that involves a Cu(I)-acetylide as a low-valent intermediate.
M. Hassink, X. Liu, J. M. Fox, Org. Lett., 2011, 13, 2388-2391.
In the presence of Ph3P and a catalytic amount of Fe(TCP)Cl, ketenes react with EDA to give allenes in high yields under neutral conditions. By employing a chiral phosphine, allenes could be synthesized with high enantioselectivity in good yields.
C.-Y. Li, X.-B. Wang, X.-L. Sun, Y. Tang, J.-C. Zheng, Z.-H. Xu, Y.-G. Zhou, L.-X. Dai, J. Am. Chem. Soc., 2007, 129, 1494-1495.
Lithiation of 1-iodo-1,3-dienyl phosphine oxides and subsequent Wittig-Horner reaction with aldehydes gives vinyl allenes in high yields. The preparation of the 1-iodo-1,3-dienyl phosphine oxides is described. This multi-step sequence allows the synthesis of vinyl allenes from two different alkynes and one aldehyde.
Z. Xi, W.-X. Zhang, Z. Song, W. Zheng, F. Kong, T. Takahashi, J. Org. Chem., 2005, 70, 8785-8789.
An efficient Cu(I)-catalyzed cross-coupling reaction of terminal alkynes and bis(trimethylsilyl)diazomethane provides 1,1-disilyl allenes through metal-carbene migratory insertion. Subsequent transformations of 1,1-disilyl allenes show interesting reactivities.
S. Xu, R. Chen, Z. Fu, Y. Gao, J. Wang, J. Org. Chem., 2018, 83, 6186-6192.
An efficient Cu(I)-catalyzed coupling of diazophosphonates with terminal alkynes provides allenylphosphonates using inexpensive CuI as the catalyst under mild conditions.
C. Wu, F. Ye, G. Wu, S. Xu, G. Deng, Y. Zhang, J. Wang, Synthesis, 2016, 48, 751-760.