1.1: trifluoroacetic acid / methanol; dichloromethane / 2 h / 20 °C 2.1: 2-cyanoethyl N,N,N',N'-tetra-isopropylphosphorodiamidite / dichloromethane / 2 h / 20 °C / Inert atmosphere; Molecular sieve 2.2: 1.5 h / 20 °C 2.3: 0.17 h / 0 - 20 °C 3.1: Pearlman's catalist; hydrogen; acetic acid / methanol / 7 h / 20 °C / 760.05 Torr View Scheme