Aldol condensation:OHC–CH₂–CH₂–COOCH₃ ⟶ HO–C(=O)–CH₂–CH(CH₃)–CH₂–C(=O)–CH₂⟶ –H₂O ⟶ 3-methylcyclopent-2-en-1-one (α,β-unsaturated cyclic ketone).