To a solution of ethyl 2-amino-4-(tetrahydro-4H-pyran-4-ylidene)butanoate (163) (1.0 g, 4.7 mmol) in anhydrous dichloromethane (30 mL) was added Hunig's base (1.6 mL, 9.4 mmol) followed by 4-nitrobenzenesulfonyl chloride (1.14 g, 5.2 mmol) and the reaction stirred at room temperature under nitrogen for 2 h. The reaction was diluted with dichloromethane and washed with 0.1 N HCl, the organic layer was dried over MgSO4 and concentrated in vacuo. The residue was purified by silica gel chromatography eluting with 10-70% hexanes/EtOAc to afford the title compound as an off-white solid in quantitative yield.
