1: 61 percent / aq. HBr / acetic acid / 3 h / Ambient temperature 2: 71 percent / triphenylphosphine, diethyl azodicarboxylate / tetrahydrofuran / 90 h / Ambient temperature 3: 74 percent / CF3COOH / CH2Cl2 / 3 h / Ambient temperature View Scheme

hydrogen bromide in acetic acid 3 h; Ambient temperature;