[Cl:1][C:2]1[CH:3]=[C:4]([N+:14]([O-:16])=[O:15])[C:5]([C:8]#CC(C)(O)C)=[N:6][CH:7]=1.[O-:17][Mn](=O)(=O)=O.[K+].[OH-:23].[Na+]>O>[Cl:1][C:2]1[CH:3]=[C:4]([N+:14]([O-:16])=[O:15])[C:5]([C:8]([OH:17])=[O:23])=[N:6][CH:7]=1A suspension of the alkyne from step 1 (1.96 g, 8.2 mmol) in water (20 mL) was heated at 75-80° C. KMnO4 (4.27 g, 27.1 mmol) was added portion wise over 30 min. After complete addition, heating was continued for 45 min. The reaction mixture was then cooled to room temperature and the pH adjusted to 9 by the addition of 1.0 M aqueous NaOH and filtered through filter paper. The filter cake was thoroughly washed with 0.3 M aqueous NaOH. The filtrate was extracted with EtOAc and discarded. The aqueous part was acidified to pH 3-4 with 1 M HCl and saturated with solid NaCl. This solution was extracted with EtOAc (4×30 mL). The combined extract was dried (Na2SO4) and concentrated under reduced pressure to provide the crude acid (500 mg). MS m/z: 200.8 (M−H).
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