[CH2:1]([O:3][C:4](=[O:19])[CH:5]([CH2:10][C:11](=O)[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1)[C:6](=[O:9])[CH2:7][CH3:8])[CH3:2].[OH-].[Na+].CCOCC>C(O)C>[CH2:1]([O:3][C:4]([CH:5]1[CH2:10][C:11]([C:12]2[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=2)=[C:7]([CH3:8])[C:6]1=[O:9])=[O:19])[CH3:2]A solution of the diketoester 20a (12 g, 45.8 mmol) in dry ethanol (150 ml) was added dropwise to a solution of sodium hydroxide (1.83 g, 45.8 mmol) in dry ethanol (75 ml) with vigorous stirring. The solution was heated to 50° C. and stirred overnight at that temperature. Ether (1.5 L) was added and the organic phase was washed with 2 N HCl (3×300 ml) and dried over anhydrous sodium sulfate. The solvent was removed in vacuo to give an oil that was purified by flash column chromatography (6% EtOAc/hexane) to give the cyclic β-ketoester 21a (8.7 g, 78%) as a yellow oil: TLC Rf=0.40 (silica gel, 25% EtOAc/hexane); 1H NMR (400 MHz, CDCl3) δ 7.56-7.52 (m, 2H), 7.50-7.42 (m, 3H), 4.26 (q, J=7.2 Hz, 2H), 3.58 (dd, J=3.2 Hz, 7.6 Hz, 1H), 3.38-3.31 (m, 1H), 3.15-3.07 (m, 1H), 1.99 (s, 3H), 1.32 (t, J=7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 202.6, 169.6, 166.5, 135.8, 134.9, 130.2, 128.9, 127.9, 61.9, 51.3, 33.7, 14.5, 10.5; HRMS calcd for C15H16O3+Na+ 267.0997; found 267.0974 [M+Na+].
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