Nickel-Catalyzed Addition of Alkynylboranes to Alkynes

Significance

Organoboranes are valuable synthetic intermediates in synthesis, and this report describes the stereoselective addition (cis) of alkynylboranes to alkynes. Pd catalysis did not afford any alkynylboration product while Ni(cod)₂ proved to be the optimal catalyst. Of the many phosphine ligands tested PCy₃ provided the best results while PMe₃ showed no activity. Slow addition of the alkyne to the alkynylborane proved necessary to reduce oligomerization of the alkyne. Another attractive feature of this protocol is the regio­selective addition to unsymmetrical alkynes.