1: 2-[N-[[(9-fluorenyl)methoxy]carbonyl]amino]-2-(isopropylthio)acetic acid With N-bromosuccinmide in tetrahydrofuran T=0°C; 0.5 h; 2: carbamic acid 1,1-dimethylethyl ester in tetrahydrofuran T=0°C; 12 h; Further stages.;