Cl.[CH3:2][O:3][C:4](=[O:11])[C@H:5]([C:7]([CH3:10])([CH3:9])[CH3:8])[NH2:6].[C:12]([O-:15])(O)=O.[Na+].C(Cl)(Cl)=O.C1(C)C=CC=CC=1.[CH:28]([NH:31][CH2:32][CH2:33][CH2:34][CH:35]=[CH2:36])([CH3:30])[CH3:29]>C1COCC1.CCOC(C)=O>[CH:28]([N:31]([CH2:32][CH2:33][CH2:34][CH:35]=[CH2:36])[C:12]([NH:6][C@H:5]([C:4]([O:3][CH3:2])=[O:11])[C:7]([CH3:10])([CH3:9])[CH3:8])=[O:15])([CH3:30])[CH3:29]To a solution (60 nM) of L-tert-leucine methyl-ester hydrochloride and NaHCO3 (8 eq) in dry THF, a solution 20% w/w of phosgene in toluene (5 eq) was added dropwise at 0° C. and the reaction mixture was stirred at that temperature for 30 minutes. Then the solid was filtered-off and the filtrate evaporated at reduced pressure. The resulting crude yellow oil was taken-up in dry THF (0.3 M) and added dropwise to a stirred solution (0.2 M) of N-isopropylpent-4-en-1-amine and TEA (1 eq). The reaction mixture was stirred at room temperature overnight. Then the mixture was taken-up in EtOAc and washed twice with water and brine. The organic phase was dried over Na2SO4 and the volatiles evaporated at reduced pressure. The crude was purified by flash chromatography eluting with petroleum ether (8) EtOAc (2) using Nynhydrin as stain. Methyl N-{[isopropyl(pent-4-en-1-yl)amino]carbonyl}-3-methyl-L-valinate was obtained as light yellow oil (43%).
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