phosphorus tribromide T=40 - 50°C; 192 h;

1: 76 percent / piperidine, pyridine / 15 h / 100 °C 2: 89 percent / 6 N aq. HCl / 19 h / Heating 3: 1.) ethyl chloroformate, Et3N, 2.) aq. NaBH4 / 1.) THF, RT, 1 h, 2.) THF, 1 h 4: 97 percent / PBr3 / 192 h / 40 - 50 °C View Scheme

1: 76 percent / piperidine, pyridine / 15 h / 100 °C 2: 89 percent / 6 N aq. HCl / 19 h / Heating 3: 1.) ethyl chloroformate, Et3N, 2.) aq. NaBH4 / 1.) THF, RT, 1 h, 2.) THF, 1 h 4: 97 percent / PBr3 / 192 h / 40 - 50 °C View Scheme