1: 30percent H2O2, saturated NaHCO3 / tetrahydrofuran / 0.5 h / 25 °C 2: acetone / 2 h / -42 °C 3: CrO3, pyridine / CH2Cl2 / 0.33 h 4: 2.5percent aq. citric acid / methanol / 0.5 h / 25 °C View Scheme

dihydrogen peroxide; sodium hydrogencarbonate in tetrahydrofuran T=25°C; 0.5 h; Yield given;