1: 53 percent / guanidine / propan-2-ol; tetrahydrofuran / 1 h 2: 97 percent / Br2 / CH2Cl2 / 1 h / 0 °C 3: 81 percent / aq. TFA 4: 95 percent / NaBH4 / ethanol View Scheme

1,8-diazabicyclo[5.4.0]undec-7-ene in tetrahydrofuran 16 h; Heating;