Cycloaddition of Alkynes and Heterocumulenes

Hoberg, Burkhart, and co-workers pioneered the field of Ni-mediated reactions of alkynes and heterocumulenes. Through studying stoichiometric reactions, they were able to show that alkynes and a variety of heterocumulenes undergo oxidative coupling with Ni(0) complexes to afford isolable nickelacycles. For example, they showed that 

In addition to stoichiometric studies with CO2, Hoberg and Oster also investigated the reactivity of isocyanates. Not surprisingly, he found the reactivity of isocyanates mirrors the reactivity of CO2. For example, he found that when diphenylacetylene and phenyl isocyanate were combined with Ni(0) and TMEDA, a five-membered 

The other congener in the class of heterocumulenes, ketene, is perhaps the least studied and most challenging coupling partner. Unlike the studies outlined above, no data on nickel-mediated oxidative coupling between ketenes and alkynes currently exists. Similarly, no data exist on ketene insertion into a five-membered nickelacycle arising from homooxidative coupling of two alkynes. However, a handful of 

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