hydrogen bromide; acetic anhydride in chloroform; water; acetic acid Ambient temperature; Yield given;

1: 74 percent / triethylamine / benzene; dioxane / 4 h / 0 °C 2: 1.) 90percent trifluoroacetic acid; 2.) sulphuric acid / 1.) ethanol, chloroform, 10 min, room t.; 2.) 4 h, room t. 3: hydrogen bromide, acetic anhydride / acetic acid; H2O; CHCl3 / Ambient temperature View Scheme

1: 1.) 90percent trifluoroacetic acid; 2.) sulphuric acid / 1.) ethanol, chloroform, 10 min, room t.; 2.) 4 h, room t. 2: hydrogen bromide, acetic anhydride / acetic acid; H2O; CHCl3 / Ambient temperature View Scheme

1: 91 percent 2: 74 percent / triethylamine / benzene; dioxane / 4 h / 0 °C 3: 1.) 90percent trifluoroacetic acid; 2.) sulphuric acid / 1.) ethanol, chloroform, 10 min, room t.; 2.) 4 h, room t. 4: hydrogen bromide, acetic anhydride / acetic acid; H2O; CHCl3 / Ambient temperature View Scheme

1: 74 percent / dicyclohexyl-18-crown-6 / acetonitrile / Ambient temperature 2: 47 percent / Dowex-1 (basic) resin / methanol / Ambient temperature View Scheme