Trifluoroacetic acid → (S)-1-[(S)-2-tert-Butoxycarbonylamino-3-(tert-butyl-diphenyl-silanyloxy)-propionyl]-hexahydro-pyridazine-3-carboxylic acid 2,2,2-trichloro-ethyl ester

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Reaction Steps

To (S)-tetrahydro-pyridazine-1,2,3-tricarboxylic acid 1,2-di-tert-butyl ester 3-(2,2,2-trichloro-ethyl) ester (prepared according to the procedure described in Angew. Chem. Int. Ed. English 1999, 38, 2443.), (5.0 g, 10.8 mmol) in anhydrous dichloromethane (33 mL) at 0° C. and under an atmosphere of nitrogen was added trifluoroacetic acid (33 mL, 432 mmol). The solution was warmed to room temperature and stirred for 16 h. The reaction was concentrated in vacuo and the residue co-evaporated from toluene (3×). The resulting brown viscous oil was dissolved in anhydrous acetonitrile (5 mL) and added to a solution of (S)-2-tert-butoxycarbonylamino-3-(tert-butyl-diphenyl-silanyloxy)-propionic acid (2.39 g, 5.4 mmol, prepared as in PCT Int. Appl. 2006, WO 2006004880 A2), N,N-diisopropylethylamine (3.76 mL, 21.6 mmol) and O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (2.05 g, 5.4 mmol) in anhydrous acetonitrile (25 mL) that had been previously stirred at 0° C. for 20 minutes. The reaction was warmed to room temperature and stirred for 16 h before being concentrated in vacuo. The residue was purified by silica gel chromatography using iso-hexanes/ethyl acetate 4:1 to give the title compound (1.8 g, 49%) as a clear viscous oil. 1H NMR (300 MHz, CDCl3) δ 1.08 (s, 9H), 1.46 (s, 9H), 1.53-1.67 (m, 1H), 1.80-2.01 (m, 2H), 2.82-2.96 (m, 1H), 3.19-3.32 (m, 1H), 3.62 (d, J=10.9 Hz, 1H), 3.80-3.97 (m, 3H), 4.23-4.34 (m, 1H), 4.61 (d, J=12.0 Hz, 1H), 4.90 (d, J=12.0 Hz, 1H), 5.18-5.27 (m, 1H), 5.51-5.63 (m, 1H), 7.35-7.49 (m, 6H), 7.58-7.70 (m, 4H). LCMS (m/z) 686.2 [M+H], Tr=4.32 min.

Provenance & Evidence