Nicholas reaction, Cobalt–alkyne complexes, Cycloheptyne, Propargyl cations
Nicholas reactions on the cation derived from the cyclic allylic acetate alkynedicobalt complex 1 favour the gamma-site kinetically for most nucleophiles, with increasing amounts of of-products in cases with greater nucleophilicity. Some regiocontrol in introduction of a specific nucleophilic fragment is possible by using different nucleophiles. Under conditions where reversibility is possible, the thermodynamically favoured site is exclusively gamma-. (c) 2005 Elsevier Ltd. All rights reserved.
DiMartino, Joseph and Green, James R.. (2006). Lewis and protic acid mediated Nicholas reactions of 3-acetoxycyclohept-1-en-4-ynedicobalt hexacarbonyl: site selectivity of nucleophile incorporation. Tetrahedron, 62 (7), 1402-1409.