[C:1]([CH2:5][C:6]([O:8][CH2:9][CH3:10])=[O:7])(=[O:4])[CH2:2][CH3:3].[H-].[Na+].Br[CH2:14][C:15]([C:17]1[CH:22]=[CH:21][C:20](C)=[CH:19][N:18]=1)=[O:16].[Cl-].[NH4+]>C1COCC1>[CH2:9]([O:8][C:6](=[O:7])[CH:5]([CH2:14][C:15](=[O:16])[C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][N:18]=1)[C:1](=[O:4])[CH2:2][CH3:3])[CH3:10]
Ethyl propionylacetate 18 (5 g, 34.7 mmol) was added slowly to a stirred suspension of sodium hydride (60% dispersion in mineral oil, 1.665 g, 41.65 mmol, 1.2 equiv) in THF (50 ml) at 0° C. and the mixture was stirred for 30 min. Compound 19b (8.092 g, 38.17 mmol, 1.1 equiv) in THF (5 ml) was added dropwise and the reaction mixture was stirred at room temperature for 16 h. Saturated aqueous ammonium chloride (30 ml) was added and the mixture was subsequently extracted with diethyl ether (3×30 ml). The combined organic layers were washed with brine and dried over anhydrous sodium sulfate. The solvent was removed in vacuo to give a dark yellow oil that was purified by flash column chromatography (10% EtOAc/hexanes) to give the diketoester 20b (7.3 g, 76%) as a yellow oil: TLC Rf=0.33 (silica gel, 20% EtOAc/hexane); 1H NMR (400 MHz, CDCl3) δ 8.50 (broad s, 1H), 7.89 (d, J=8.0 Hz, 1H), 7.66 (dd, J=1.6 Hz, 8.0 Hz, 1H), 4.20 (q, J=7.2 Hz, 2H), 4.15 (dd, J=6.0 Hz, 8.0 Hz, 1H), 3.92 (dd, J=8.4 Hz, 18.8 Hz, 1H), 3.74 (dd, J=6.0 Hz, 18.8 Hz, 1H), 2.85-2.66 (m, 2H), 2.41 (s, 3H), 1.27 (t, J=7.2 Hz, 3H), 1.10 (t, J=7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 205.5, 198.9, 169.6, 150.7, 149.8, 138.1, 137.3, 121.7, 61.8, 53.5, 37.1, 36.2, 18.9, 14.2, 7.9; HRMS calcd for C15H19NO4+Na+ 300.1212; found 300.1200 [M+Na+].
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