Carbocyclic ring expansions with alkyne and carbene sources mediated by nickel(0) complexes: Structure of the critical organonickel intermediates

Experimental evidence is assessed concerning the nature of organonickel intermediates involved in the cyclotrimerization and the cyclotetramerization of alkynes, as well as the cross-oligomerization of alkynes with carbene sources, as mediated by nickel(0) complexes. In the former processes a sequential series of nickelacycloalkapolyenes are the productive intermediates and in the latter cross-oligomerizations nickel(0)-carbene complexes themselves are critical precursors to the ultimately generated carbocycles. (C) 1998 Elsevier Science Ltd. All rights reserved.