1: 97 percent / Ph3P, DEAD / tetrahydrofuran / 0.5 h / Ambient temperature 2: 82 percent / K2CO3 / methanol / 1 h / Ambient temperature 3: 92 percent / Et3N / CH2Cl2 / 0.5 h / 0 °C 4: 83 percent / Na2S*9H2O, sulfur / dimethylformamide / 2.42 h / 80 °C 5: 70 percent / aq. KOH / methanol / 3 h / Ambient temperature View Scheme

1: Et3N / CH2Cl2 2: Na2S*9H2O, S / dimethylformamide 3: 53 percent / 0.1 M KOH / H2O / 20 h / Ambient temperature; darkness View Scheme

triphenylphosphine; diethylazodicarboxylate in tetrahydrofuran 0.5 h; Ambient temperature;