A mixture of [PtCl 2(CH 2CH 2)] 2 (1 mol %), and EuCl 3 (2 mol %) catalyzes the hydroalkylation of 4-pentenyl β-dicarbonyl compounds to form substituted cyclohexanones in moderate to excellent yield with excellent regioselectivity. Reaction of 5,5-dimethyl-8-nonene-2,4-dione with a catalytic mixture of [PtCl 2(CH 2CH 2)] 2 (2) (1 mol %), and EuCl 3 (2 mol %) in dioxane that contained HCl (1.0 equiv) at 90°C for 18 h led to the isolation of 2-acetyl-3,6,6-trimethyl-2-cyclohexanone in 85% yield. A number of 4-pentenyl β-dicarbonyl compounds underwent intramolecular hydroalkylation to form cyclohexanones in moderate to excellent yield. © 2004 Elsevier Ltd. All rights reserved.