1: ozone / 0.25 h / -78 - 25 °C / |Inert atmosphere 2: methanol; acetic acid / 3 h / |Inert atmosphere; |Reflux 3: potassium carbonate / methanol / 1 h / 20 °C / |Inert atmosphere 4: triphenylphosphine; di-isopropyl azodicarboxylate / tetrahydrofuran / -10 - 20 °C / |Inert atmosphere 5: sodium methylate / methanol / |Inert atmosphere View Scheme