Synthesis of allenes

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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.

A. Tsubouchi, T. Kira, T. Takeda, Synlett, 2006, 2577-2580.

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.

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.

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 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.

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.

The facile iodolactonisation of ethyl 2,3-allenoates with I₂ in aqueous MeCN gave 4-iodofuran-2(5H)-ones in moderate to high yields.
C. Fu, S. Ma, Eur. J. Org. Chem., 2005, 3942-3945.

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.