[H-].[Na+].[C:3]([O:7][C:8]([N:10]1[CH2:14][CH2:13][CH2:12][CH:11]1[CH:15]=O)=[O:9])([CH3:6])([CH3:5])[CH3:4].CCCCCC.[CH3:23][CH2:24][O:25][C:26]([CH3:28])=[O:27]>C1COCC1.CCOC(C)=O.[Cl-].[Na+].O>[C:3]([O:7][C:8]([N:10]1[CH2:14][CH2:13][CH2:12][CH:11]1[CH:15]=[CH:28][C:26]([O:25][CH2:24][CH3:23])=[O:27])=[O:9])([CH3:4])([CH3:5])[CH3:6]
A 2 L, 3-necked round bottomed flask equipped with an overhead stirred and nitrogen inlet was charged with NaH (60%, 10.0 g, 0.25 mol) and anhydrous THF (200 mL). To the stirred mixture was slowly added triethylphosphonoacetate (53.8 g, 0.24 mol) over 20 minutes. A solution of crude 2-formyl-pyrrolidine-1-carboxylic acid tert-butyl ester (40 g, 0.20 mol) in THF (75 mL) was added dropwise. The solution turned orange and the stirring was continued for 1 h until no aldehyde remained by TLC analysis [1:1 hexane/EtOAc, Rf(aldehyde)=0.6; Rf(14)=0.8]. The solution was diluted with EtOAc and brine and the layers were separated. The EtOAc layer was washed with 1M HCl, brine, dried over anhydrous Na2SO4, filtered, and concentrated to afford 14 (67 g) as a yellow oil which was used without further purification. 1H NMR (CDCl3, 300 MHz) δ6.92-6.76 (m, 1H), 5.82 (d, 1H), 4.56-4.32 (m, 1H), 4.25-4.12 (m, 2H), 3.48-3.27 (m, 2H), 2.20-1.98 (m, 1H), 1.91-1.72 (m, 2H), 1.43 (s, 9H), 1.25 (t, 3H) ppm.
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