Diisopropylethylamine → 1H-Indole-2-carboxylic acid, 1-[2-[[(1,1-dimethylethoxy)carbonyl]amino]-3-methyl-1-oxobutyl]-2,3-dihydro-, ethyl ester, [S-(R*,R*)]-

Participants

Reaction Steps

N,N,N′,N′-tetramethylfluoroformamidinium hexafluorophosphate (1.1 g, 4.18 mmol, Eq: 1.6) was added to a solution of (S)-2-(tert-butoxycarbonylamino)-3-methylbutanoic acid (738 mg, 3.4 mmol, Eq: 1.3) and diisopropylethylamine (1.4 mL, 7.84 mmol, Eq: 3) in DCM (10 mL) and the resulting solution was stirred at rt for 1 h. (S)-Ethyl indoline-2-carboxylate (0.5 g, 2.61 mmol, Eq: 1.00) was added and the reaction mixture was stirred at rt over the weekend. The reaction mixture was diluted with EtOAc (50 mL) and washed with 0.1 M aqueous HCl (50 mL), 0.1 M aqueous NaOH (50 mL) and brine (25 mL). The crude material was purified by flash chromatography (silica gel, 24 g, 0% to 20% EtOAc in hexanes) to give (S)-ethyl 1-((S)-2-(tert-butoxycarbonylamino)-3-methylbutanoyl)indoline-2-carboxylate (0.58 g), m/z=391 (M+H).

Provenance & Evidence