1: (S)-1-(2,2,2-Trifluoro-acetyl)-piperidine-2-carboxylic acid (S)-3,4,4-trimethyl-2-oxo-tetrahydro-furan-3-yl ester With sodium hydroxide in tetrahydrofuran; water T=20°C; 12 h; 2: di-tert-butyl dicarbonate With sodium hydroxide in 1,4-dioxane; water T=20°C; 12 h; Title compound not separated from byproducts;

1: (S)-1-(2,2,2-Trifluoro-acetyl)-piperidine-2-carboxylic acid (S)-3,4,4-trimethyl-2-oxo-tetrahydro-furan-3-yl ester With sodium tetrahydroborate in ethanol 1.5 h; 2: di-tert-butyl dicarbonate With sodium hydroxide in 1,4-dioxane; water T=20°C; 12 h; Title compound not separated from byproducts;

1: (S)-1-(2,2,2-Trifluoro-acetyl)-piperidine-2-carboxylic acid (S)-3,4,4-trimethyl-2-oxo-tetrahydro-furan-3-yl ester With sodium tetrahydroborate in ethanol 1.5 h; 2: di-tert-butyl dicarbonate With sodium hydroxide in 1,4-dioxane; water T=20°C; 12 h; Title compound not separated from byproducts;

1: (S)-1-(2,2,2-Trifluoro-acetyl)-piperidine-2-carboxylic acid (S)-3,4,4-trimethyl-2-oxo-tetrahydro-furan-3-yl ester With sodium hydroxide in tetrahydrofuran; water T=20°C; 12 h; 2: di-tert-butyl dicarbonate With sodium hydroxide in 1,4-dioxane; water T=20°C; 12 h; Title compound not separated from byproducts;