1: 83.6 percent / dimethylsulfoxide, oxalyl chloride / CH2Cl2 / 2 h / -70 °C 2: 17.4 percent / Me3Al, 2,4,6-tri-tert-butylphenol / hexane; toluene; diethyl ether / 1.5 h / -78 °C 3: 94.5 percent / tetra-n-butylammonium fluoride / tetrahydrofuran / 0.33 h 4: 95.6 percent / NH3 / methanol / 48 h / 100 °C View Scheme