C(Cl)(=O)C(Cl)=O.CS(C)=O.[C:11]([O:15][C:16](=[O:24])[NH:17][CH2:18][C:19]1([CH2:22][OH:23])[CH2:21][CH2:20]1)([CH3:14])([CH3:13])[CH3:12].CCN(CC)CC>C(Cl)Cl.O>[C:11]([O:15][C:16](=[O:24])[NH:17][CH2:18][C:19]1([CH:22]=[O:23])[CH2:20][CH2:21]1)([CH3:12])([CH3:14])[CH3:13]
Under an argon atmosphere oxalyl chloride (1.17 mL, 13.8 mmol) was dissolved in DCM (30 mL) and cooled to −70 C. DMSO (1.95 mL, 27.6 mmol) in DCM (2.5 mL) was added over 5 min and stirred for 10 min. (1-Hydroxymethyl-cyclopropylmethyl)-carbamic acid tert-butyl ester (2.6 g, 12 mmol) in DCM (8.5 mL) was added at −70 C over 5 min and the mixture was stirred for 30 min. Et3N (6.4 mL, 45.6 mmol) was added over 5 min and the temperature was allowed to reach RT over 1 h. H2O was added and the aqueous phase was extracted with DCM (×2). The combined organic phases were washed with brine, dried over Na2SO4, filtered and concentrated in vacuo. The crude product was purified by flash chromatography on silica using heptane:EtOAc 1:15 as eluent to afford (1-Formyl-cyclopropylmethyl)-carbamic acid tert-butyl ester (0.65 g) as an oil.
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