Ionic liquids (ILs) are suitable media for the Co-2(CO)(8)-catalysed intramolecular and intermolecular Pauson-Khand (PK) annelation, provided that the reaction is carried out under a CO pressure of 10 bar. Two diethyl allyl propargyl malonates were quantitatively converted into the relevant cyclopentenones, whereas heteroatom tethered enynes gave lower yields in their cyclocarbortylation products. A moderate yield in the corresponding Pauson-Khand product was obtained reacting phenylacetylene with norbornene. (C) 2004 Elsevier B.V. All rights reserved.