1: 93 percent / NaBH4 / tetrahydrofuran; ethanol / 3 h / 20 °C 2: 1) t-BuOK / 1) THF, -40 deg C, 10 min, 2a) -40 deg C, 15 min, 2b) to 0 deg C 3: 5 percent aq. HClO4 / dioxane / Heating View Scheme

1: 1) t-BuOK / 1) THF, -30 deg C, 10 min, 2a) -20 deg C, 30 min, b) to 0 deg C 2: 93 percent / 20percent aq. H2SO4 / tetrahydrofuran / 2 h / Heating; other Δ16,20-20-isocyanopregnanes View Scheme