1: tetrabutyl ammonium fluoride / tetrahydrofuran / 0.25 h / Reflux 2: triethylsilane; boron trifluoride diethyl etherate / methanol; dichloromethane / 0.5 h / 20 °C View Scheme

1.1: oxalyl dichloride; dimethyl sulfoxide / dichloromethane / 0.67 h / -70 - -35 °C 1.2: 0.5 h / -35 - -5 °C 2.1: tetrahydrofuran / 0.25 h / 0 °C / Inert atmosphere 3.1: oxalyl dichloride; dimethyl sulfoxide / dichloromethane / 0.67 h / -70 - -35 °C 3.2: 0.5 h / -35 - -5 °C 4.1: sodium hydride / N,N-dimethyl-formamide; mineral oil / 3 h / 20 - 90 °C / Inert atmosphere 5.1: water; sodium hydroxide / methanol / 1 h / 20 °C View Scheme

tetrabutyl ammonium fluoride in tetrahydrofuran 0.25 h; Reflux; stereoselective reaction;