1.1: triphenylphosphine / toluene / 3 h / Reflux 2.1: 4-(N,N-dimethlyamino)pyridine; triethylamine / dichloromethane / 0 - 20 °C 3.1: boron trifluoride diethyl etherate / 3 h / -20 °C / Inert atmosphere 4.1: trifluoroacetic acid / dichloromethane / 1 h / 20 °C 4.2: 4 °C View Scheme