A mixture of trans-2-(5-fluoro-pyridin-2-yl)-cyclopropanecarboxylic acid HCl salt (217 mg, 1 mmol) in thionyl chloride (2 mL) was heated at reflux for over night. The mixture was concentrated and dried under high vacuum for 3 h. Then the residue was dissolved in DCM (4 mL) and added dropwise to a solution of ((1S,2S)-1-{[4-(t-butyl-dimethyl-silanyloxy)-phenylamino]-methyl}-2-methyl-butyl)-carbamic acid tert-butyl ester (422 mg, 1 mmol) and triethyl amine (409 uL, 3 mmol) in DCM (4 mL). The resulting mixture was stirred at rt for overnight. The reaction mixture was concentrated and the residue was subjected to ISCO (40 g column, 0-40% EtOAc in hexane over 40 min.) to give the titled compound (486 mg, 83%). MS (MH+ 586).
