[OH:1][C:2]1([C:13]2[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=2[CH3:19])[CH2:5][N:4]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])[CH2:3]1.[H-].[Na+].Br[CH2:23][CH:24]1[CH2:26][CH2:25]1.[Cl-].[NH4+]>CN(C)C=O>[CH:24]1([CH2:23][O:1][C:2]2([C:13]3[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=3[CH3:19])[CH2:5][N:4]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])[CH2:3]2)[CH2:26][CH2:25]13 g (11.4 mmol) of tert-butyl 3-hydroxy-3-o-tolylazetidine-1-carboxylate in 20 ml of N,N-dimethylformamide are added dropwise to a suspension of 1.4 g of sodium hydride at 60% in oil (34.2 mmol) in 14 ml of N,N-dimethylformamide, precooled to 0° C. After stirring for 20 minutes, 1 ml of bromomethylcyclopropane (11.4 mmol) is added and stirring is continued for 1 hour 30 minutes. The reaction medium is hydrolysed with saturated aqueous ammonium chloride solution and then extracted with a 1/1 heptane/ethyl acetate mixture. The organic phase is washed with saturated aqueous sodium chloride solution, dried over sodium sulfate, filtered and concentrated under vacuum. 4 g of crude residue are obtained and are purified by chromatography on silica gel eluted with a heptane/ethyl acetate mixture, the polarity being increased from 95/5 to 80/20. 2.9 g (81%) of tert-butyl 3-cyclopropylmethoxy-3-o-tolylazetidine-1-carboxylate are obtained in the form of a yellow oil.
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