1: (S)-1,2,3,4-tetrahydronaphthalen-1-aminium (1S,3aR,6aS)-2-(t-butoxycarbonyl)octahydrocyclopenta[c]pyrrole-1-carboxylate With sodium hydrogen sulphate in tert-butyl methyl ether; water 0.5 h; 2: tert-butyl alcohol With 4-(N,N-dimethlyamino)pyridine; sodium hydrogen sulphate; di-tert-butyl dicarbonate in tert-butyl methyl ether; water T=20 - 25°C; 5 - 6 h; 3: oxalic acid With methanesulfonic acid; potassium carbonate Product distribution / selectivity; more than 3 stages;