A simple and mild catalytic coupling reaction of propargyl halides with organotitanium reagents is reported. The reaction of propargyl bromide with organo-titanium reagents mediated by NiCl2 (2 mol%) and PCy3 (4 mol%) in CH2Cl2 afforded coupling product allenes in good to excellent yields (up to 95%) at room temperature. However, NiCl2(PPh3)2 was the best catalyst for substituted propargyl halides to yield allenes or alkynes preferentially. On the basis of the experimental results, a possible catalytic cycle has been proposed.

The complete synthesis of the ganglioside Hp-s1 (1) is described in 10 steps.

Nickel-Catalyzed Substitution Reactions of Propargyl Halides with Organotitanium Reagents. -The title reaction affords monosubstituted, 1,1-disubstituted or 1,3-disubstituted allenes (III), (V), or (VII) as well as substituted alkynes (IX) depending of the type of substituents on the propargyl halide. -(LI, Q.-H.; LIAO, J.-W.; HUANG, Y.-L.; CHIANG, R.-T.; GAU*, H.-M.; Org. Biomol. Chem. 12 (2014) 38, 7634-7642, http://dx.doi.org/10.1039/C4OB00677A ; Dep. Chem., Natl. Chung Hsing Univ., Taichung 402, Taiwan; Eng.) -M. Paetzel 09-074