1: 73 percent / N-ethylmorpholine, isobutyl chloroformate / tetrahydrofuran / 1 h / -15 - 20 °C 2: HBr / trifluoroacetic acid 3: 70 percent / acetonitrile / 24 h 4: 88 percent / methanol; diethyl ether / 0.08 h / Ambient temperature View Scheme

1: 73 percent / N-ethylmorpholine, isobutyl chloroformate / tetrahydrofuran / 1 h / -15 - 20 °C 2: HBr / trifluoroacetic acid 3: 70 percent / acetonitrile / 24 h View Scheme

1: N-ethylmorpholine, isobutylchloroformate / tetrahydrofuran / -15 - 20 °C 2: 1.) 5.6N HBr/AcOH, 2.) Dowex 1x8 (AcO(1-) form) / 1.) room temperature, 1h, 2.) to the negative reaction for Br(1-) ions View Scheme