1: tetrahydrofuran; cyclohexane / 15 h / -78 °C 2: 94 percent Turnov. / NaBH4 / methanol / 3 h / 25 °C 3: 86 percent Turnov. / NaN(SiMe3)2 / tetrahydrofuran / 0.5 h / 0 °C 4: 80 percent / HF*pyridine / tetrahydrofuran / 1.25 h / 25 °C View Scheme