Regioselective oxidative dehydrodimerization of the E isomers of alkoxy-, alkyl-, and halogen-substituted cinnamic acids in the system CF₃COOH-CH₂Cl₂-PbO₂ leads to formation of bis-lactones of the furo[3,4-c]furan series with similar steric structures, regardless of the substituents in the aryl fragments of the initial acids.