1: 2-(benzhydrylidene-amino)-3-mercapto-propionic acid tert-butyl ester With potassium hexamethylsilazane in tetrahydrofuran T=-78°C; 1 h; Inert atmosphere; 2: Togni’s reagent With Zn(NTf2)2 in tetrahydrofuran T=-78°C; 0.5 h; 3: With sulfuric acid in 1,4-dioxane 12 h; Reflux;