1: (3S,5S)-3-isopropyl-5-((2S,4S)-4-isopropyl-5-oxo-tetrahydro-furan-2-yl)pyrrolidin-2-one With 4-(N,N-dimethlyamino)pyridine; triethylamine in isopropanol acetate T=40 - 45°C; 2: di-tert-butyl dicarbonate in isopropanol acetate T=40 - 45°C;