Synthesis of allenes

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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.

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.

A well-designed, electron deficient, and sterically hindered amide-type NN₂ pincer ligand was crucial to the success of a general, efficient, and practical nickel-catalyzed deaminative allenylation of amino acid derivatives with terminal alkynes under mild conditions. The reaction offers good scalability, broad substrate scope, and functional group tolerance.
X. Zhang, C. Jiao, D. Qi, X. Liu, Z. Zhang, G. Zhang, Org. Lett., 2022, 24, 5361-5365.

Synthesis of Allenyl Esters by Horner-Wadsworth-Emmons Reactions of Ketenes Mediated by Isopropylmagnesium Bromide
S. Sano, T. Matsumoto, T. Yano, M. Toguchi, M. Nakao, Synlett, 2015, 26, 2135-2138.

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.

Racemic homoallenyl alcohols can be synthesized from aldehydes and chloroprene-derived Grignards. The use of bis[2-dimethylaminoethyl]ether (BDMAEE) as an additive at low temperatures shifts the selectivity of the reaction almost exclusive toward allene formation. Simple and more elaborate methods for further derivatization enable quick access to more complex structures.
A. G. A. Geissler, B. Breit, Org. Lett., 2021, 23, 2621-2625.

2,2'-Dimorpholinodiethyl ether (DMDEE) mediates a γ-selective addition of chloroprene Grignards to aromatic N-Boc aldimines to provide the corresponding N-Boc protected β-allenylamines in good yields and regioselectivities. Transmetalation to zinc bromide also allows the addition of chloroprene Grignard to aliphatic aldimines in good yields.
A. G. A. Geissler, B. Breit, Org. Lett., 2022, 24, 7967-7971.

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.

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.

A Pd-catalyzed reaction of vinyl bromides and trifluoromethylated diazoalkanes provides trifluoromethylated, tetrasubstituted allenes in very good yield under mild reaction conditions. This reaction proceeds via oxidative addition of Pd(0) to the vinyl bromide followed by base-promoted reductive elimination. An acid catalyzed cyclization of the allenes gives trifluoromethylated indenes.
C. Pei, Z. Yang, R. M. Koenigs, Org. Lett., 2020, 22, 7300-7304.

A palladium-catalyzed reaction of chloroprene (2-chloro-1,3-butadiene) with soft nucleophiles provides several functionalized terminal allenes in good yield.
M. Ogasawara, H. Ikeda, T. Nagano, T. Hayashi, Org. Lett., 2001, 3, 2615-2617.

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.

Chiral spiro phosphate dirhodium complexes catalyze an asymmetric insertion of alkynyl carbenes derived from readily available sulfonylhydrazones into the Si-H bonds of silanes to afford various chiral propargylsilanes with excellent enantioselectivity. Subsequently, a platinum catalyst was used for stereospecific isomerization of the chiral propargylsilanes to the corresponding chiral allenylsilanes.
L. L. Yang, J. Ouyang, H.-N. Zou, S.-F. Zhu, Q.-L. Zhou, J. Am. Chem. Soc., 2021, 143, 6401-6406.

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.

Propellanes have tremendous potential to be exploited in synthetic organic chemistry. An experimentally simple procedure provides cyclobutane-containing allenes and alkynes through a copper-catalyzed ring opening of [1.1.1]propellane and subsequent reaction with alkynes.
D. Lasányi, G. L. Tolnai, Org. Lett., 2019, 21, 10057-10062.