1: 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene With n-butyllithium in tetrahydrofuran; hexane 2: carbon dioxide With hydrogenchloride in tetrahydrofuran; hexane

1.1: 61 percent / Br2; Fe / CHCl3 / 20 °C 2.1: n-BuLi / hexane; tetrahydrofuran 2.2: 83 percent / hydrochloric acid / hexane; tetrahydrofuran View Scheme

1: 58 percent / FeCl3 / CH2Cl2 / 1.) from 0 deg C to RT, 3 h, 2.) 15 h 2: bromine / CCl4 / 1.) from 0 deg C to RT, 3 h, 2.) 23 h 3: Fe, bromine / CCl4 / 26 h / Ambient temperature 4: 1.) n-BuLi / 1.) THF, hexane, -78 deg C, 30 min, 2.) from -78 deg C to RT View Scheme

1: 96 percent / toluene / 1.) from 0 deg C to RT, 3 h, 2.) 14 h 2: 58 percent / FeCl3 / CH2Cl2 / 1.) from 0 deg C to RT, 3 h, 2.) 15 h 3: bromine / CCl4 / 1.) from 0 deg C to RT, 3 h, 2.) 23 h 4: Fe, bromine / CCl4 / 26 h / Ambient temperature 5: 1.) n-BuLi / 1.) THF, hexane, -78 deg C, 30 min, 2.) from -78 deg C to RT View Scheme

1: Fe, bromine / CCl4 / 26 h / Ambient temperature 2: 1.) n-BuLi / 1.) THF, hexane, -78 deg C, 30 min, 2.) from -78 deg C to RT View Scheme

1: 22 percent / diphenyl phosphoryl azide, triethylamine / toluene / 22 h / 80 °C 2: 65 percent / KOH / ethanol / 23 h / 100 °C 3: 28 percent / ethanol View Scheme

sodium azide; sulfuric acid in chloroform T=20 - 51°C; 2.5 h;