The Nickel-Catalyzed Carbonylative Cycloaddition of Allyl Halides and Acetylenes: An Efficient Tool for Cyclopentane Annelation

From a practical synthetic point of view, the nickel-mediated carbonylative cycloaddition of alkynes and ally halides is a straightforward method for obtaining the cyclopentane skeleton in high yields and with controlled stereochemistry, especially when considering the efficiency of the intermolecular version of the reaction. The efforts to make the previously stoichiometric process catalytic in nickel, after experimental mechanistic observations, are reported herein. The unexpected intervention of iron as a reductant and the isolation of a final dimeric species that exhibits interesting tautomeric behavior are also presented. An extension of the reaction to new substrates has led to the conclusion that, although the steric and electronic effects of the alkyne substituents arc generally irrelevant in relation to the adducts and their yields, those of the allylic counterpart may have a significant influence on the outcome of the reaction. However, the presence of the amine moiety in the alkyne completely inhibited the reaction. The feasibility of a multicentered reaction was verified with a triacetylene in which up to 12 bonds were created at once and in good yield.