1: 85 percent / isopropenyl chloroformate, 4-N,N-dimethylaminopyridine / CH2Cl2 / 3 h / -5 °C 2: 95 percent / methanol / 0.33 h / Heating 3: sodium borohydride / CH2Cl2; acetic acid / 5 h 4: 87 percent / NaOH / acetone / Ambient temperature View Scheme

Multistep reaction;

4-(N,N-dimethlyamino)pyridine; triethylamine in dichloromethane

1: N-(tert-butoxycarbonyl)phenylalanine With 2,4,6-trimethyl-pyridine; dicyclohexyl-carbodiimide in tetrachloromethane T=-20°C; 1 h; Inert atmosphere; 2: tert-butyl alcohol With (S)-(+)-1-tert-butyldiphenylsilyloxy-3-(3'-methyl-3'H-imidazol-4'-yl)-2-(2'',4'',6''-triisopropylbenzenesulfonylamino)propane in tetrachloromethane T=-20°C; 20 h; Inert atmosphere; 3: With hydrogenchloride; water in tetrachloromethane Inert atmosphere; optical yield given as percent eeenantioselective reaction;

1: With triethylamine in tetrahydrofuran T=0°C; 1 h; 2: With sodium tetrahydroborate in tetrahydrofuran; water T=0 - 20°C;

1: potassium hydrogencarbonate 2: lithium aluminium tetrahydride / 0 °C View Scheme

ytterbium(III) triflate in nitromethane T=45 - 50°C; 24 h;

1: N-(tert-butoxycarbonyl)phenylalanine With 2,4,6-trimethyl-pyridine; dicyclohexyl-carbodiimide in tetrachloromethane T=-20°C; 1 h; Inert atmosphere; 2: tert-butyl alcohol With (S)-(+)-1-tert-butyldiphenylsilyloxy-3-(3'-methyl-3'H-imidazol-4'-yl)-2-(2'',4'',6''-triisopropylbenzenesulfonylamino)propane in tetrachloromethane T=-20°C; 20 h; Inert atmosphere; 3: With hydrogenchloride; water in tetrachloromethane Inert atmosphere; optical yield given as percent eeenantioselective reaction;

1: 1-(3-dimethylaminopropyl)-3-ethylcarbodimide hydrochloride; 4-dimethylaminopyridine / CH2Cl2 / 0 - 20 °C 2: HCl / ethyl acetate / 0.5 h View Scheme