A highly chemoselective intermolecular [2 + 2 + 2] cycloaddition of 2 eq. of terminal alkynes with dimethyl acetylenedicarboxylate, which enables the straightforward synthesis of dialkylated o-phthalates, was successfully accomplished using a ruthenium catalyst, Cp*RuCl(cod) (Cp*: pentamethylcyclopentadienyl, cod: 1,5-cyclooctadiene). The co-cyclotrimerisation of alkynes and acetylenedicarboxylates usually affords 1:2 adducts (1,2,3,4-benzenetetracarboxylates), however, in the present reaction 2:1 adducts (o-phthalates) are the major products unprecedentedly. (C) 2003 Elsevier B.V. All rights reserved.