A series of Ni(OEtHex)(2)/phosphine/Et2AlCl systems were used as cycloisomerization catalysts of various 1,6-heptadienes. The best results were obtained with the catalytic system using triphenylphosphine as a ligand. The cycloisomerization with this system afforded the corresponding methyl(methylene)cyclopentane derivatives with high selectivity (40-99%) and in good overall yields of the cyclopentane derivatives (90-96%). The cycloisomerization proceeded also with other derivatives possessing 1,6-diene moiety giving the corresponding methyl(alkenyl)cyclopentane derivatives in good yields (33-90%). (c) 2007 Elsevier B.V. All rights reserved.