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Synthesis of allenes by 1,4-addition

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The combination of Pd(0)Senphos/B(C6F5)3/NR3 catalyzes an addition of ketones to 1,3-enynes to provide allenes. A wide range of aryl- and aliphatic ketones undergo addition to various 1,3-enynes in high yields at room temperature. The mechanism includes a rate-determining outer-sphere proton transfer, which was corroborated by DFT calculations.
M. Eaton, Y. Dai, Z. Wang, B. Li, W. Lamine, K. Miqueu, S.-Y. Liu, J. Am. Chem. Soc., 2023, 145, 21638-21645.


Conjugated enynes undergo selective 1,4-hydroamination under Pd catalysis to deliver chiral allenes with pendant allylic amines. Several primary and secondary aliphatic and aryl-substituted amines couple with a wide range of mono- and disubstituted enynes in a nonenantioselective reaction where DPEphos serves as the ligand. Benzophenone can be used as an ammonia surrogate.
N. J. Adamson, H. Jeddi, S. J. Malcolmson, J. Am. Chem. Soc., 2019, 141, 8574-8583.


A practical, convenient, and highly regioselective copper-catalyzed 1,4-chlorotrifluoromethylation of 1,3-enynes affords chloro- and CF3-containing tetrasubstituted allene derivatives with very good yield. A 1,4-bromotrifluoromethylation is also reported.
J. Huang, Y. Jia, X. Li, J. Duan, Z.-X. Jiang, Z. Yang, Org. Lett., 2021, 23, 2314-2319.


Cu(CH3CN)4BF4 catalyzes a radical bis(trifluoromethylation) of alkynes and 1,3-enynes with Togni reagent II and (bpy)Zn(CF3)2 at room temperature to afford the corresponding 1,2-bis(trifluoromethylated) alkenes and 1,4-bis(trifluoromethylated) allenes in good yields. This protocol exhibits broad substrate scope and excellent functional group compatibility.
H. Shen, H. Xiao, L. Zhu, C. Li, Synlett, 2020, 31, 41-44.