The invention relates to a process for the preparation, in a single step, of substituted 2-cyclopenten-1-ones by reacting a substituted enone with an aldehyde in the presence of a catalytic system. The catalytic system consists of a metal complex, such as a Ti(Cl).sub.3(alkoxy), and a co-ingredient, such as a carboxylic acid anhydride or an anhydrous salt.