1: 97 percent / CrO3, H2SO4 / acetone / 1 h / 0 - 5 °C 2: 99 percent / KOH, NaOCl / dioxane / 2.5 h 3: n-butyllithium / hexane; diethyl ether / 0.5 h / -70 °C 4: tetra-n-butylammonium fluoride / tetrahydrofuran / 0.17 h / 25 °C View Scheme