N,N,N′,N′-Tetramethyl-O-(7-azabenzotriazol-1-yl)uronium hexafluorophosphate (88 mg, 0.23 mmol) was added to a solution of (2S)-2-[(tert-butoxycarbonyl)amino]-3-(4-isopropoxyphenyl)propanoic acid (50 mg, 0.2 mmol) in N,N-dimethylformamide (5 mL) and N,N-diisopropylethylamine (54 uL, 0.31 mmol). The reaction was stirred for 10 min, and the 2.00 M of dimethylamine in tetrahydrofuran (0.4 mL, 0.6 mmol) was added. The reaction was stirred for 2 h. at r.t. and was partitioned between water and ethyl acetate. The organic phase was washed with saturated brine, dried over magnesium sulfate, filtered and concentrated under reduced pressure to give the crude product, (S)-tert-butyl 1-(dimethylamino)-3-(4-isopropoxyphenyl)-1-oxopropan-2-ylcarbamate (50 mg, 90%). Analytical LCMS (M+H-Boc)+: m/z=251.0.
