1: (4S,5S)-ethyl (4-isobutyl-2-oxo-oxazolidin-5-yl)acetate With lithium hydroxide in methanol T=20°C; 1.5 h; 2: 1-[[(9H-fluoren-9-ylmethoxy)carbonyl]oxy]-2,5-pyrrolidinedione With triethylamine in methanol T=20°C; 0.25 h; Further stages.;