1.4 ml (16.24 mmol) oxalylchloride was added to a dry-ice cooled solution (−78° C.) of 1.78 ml (25 mmol) DMSO in 40 ml CH2Cl2. After 10 min. stirring at −78° C., 2.39 g (12.49 mmol) of trans-[4-(3-Hydroxy-propyl)-cyclohexyl]-methyl-carbamic acid tert-butyl ester, dissolved in 5 ml CH2Cl2, was added. 15 min later, 8.7 ml (62.4 mmol) Et3N was added and the reaction-mixture was allowed to attain RT. The mixture was diluted with Et2O and then washed with 1N HCl and water. After evaporation of the solvents, a solution of crude trans-Methyl-[4-(3-oxo-propyl)-cyclohexyl]-carbamic acid tert-butyl ester (3.24 g, 12.02 mmol) and of 2.73 ml (13.3 mmol) triethyl phosphono acetate in 30 ml ethanol, was treated under ice-cooling with 1.37 g (24.05 mmol) NaOMe. The solution was stirred for 20 h at RT, and then concentrated in vacuo. The crude residue was dissolved in Et2O and washed with water. The organic layers were concentrated in vacuo and the crude product purified by chromatography on silica gel with EtOAc/Hexane 1:4 to yield 2.46 g (58%, 2 steps) of clean trans-5-[4-(tert-Butoxycarbonyl-methyl-amino)-cyclohexyl]-pent-2-enoic acid ethyl ester, MS: 339 (M).
