[C:1]([N:5]([CH2:14][C:15]([O:17]CC)=O)[CH2:6][CH2:7][CH2:8][C:9]([O:11][CH2:12][CH3:13])=[O:10])([CH3:4])([CH3:3])[CH3:2].CC(C)([O-])C.[K+]>O1CCCC1>[C:1]([N:5]1[CH2:6][CH2:7][CH:8]([C:9]([O:11][CH2:12][CH3:13])=[O:10])[C:15](=[O:17])[CH2:14]1)([CH3:4])([CH3:3])[CH3:2]To a solution of the product of step B (14.0 g; 50.9 mmol) in tetrahydrofuran (200 mL) was added 1.05 eq of potassium tert-butoxide (6.0 g; 53.5 mmol). The reaction was maintained at ambient temperature for 2 h and then quenched with a sufficient amount of saturated aqueous ammonium chloride to make the solution pH 8. The tetrahydrofuran was removed in vacuo and the aqueous layer was extracted three times with diethyl ether. The combined organic extracts were washed with brine, dried (Na2SO4), filtered and concentrated in vacuo to afford the title compound (7.15 g).
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