Carbonylative dimerisation of norbornene by cobalt carbonyl: an overlooked by-product of the Pauson–Khand reaction

Treatment of norbornene with either dicobaltoctacarbonyl or with preformed alkyne-dicobalthexacarbonyl complexes gives enol-lactone dimer 3, derived from carbonylative coupling of two molecules of norbornene. This product which has not been recorded before under these conditions appears likely to be an overlooked by-product of many Pauson–Khand reactions.