[CH2:1]([O:3][C:4]1[C:13]2[C:8](=[CH:9][CH:10]=[CH:11][CH:12]=2)[C:7]([O:14][CH2:15][CH3:16])=[C:6]([C:17]([O:19]CC)=[O:18])[C:5]=1[C:22]([O:24]CC)=[O:23])[CH3:2].[OH-].[Na+]>C(O)C.O>[CH2:15]([O:14][C:7]1[C:8]2[C:13](=[CH:12][CH:11]=[CH:10][CH:9]=2)[C:4]([O:3][CH2:1][CH3:2])=[C:5]([C:22]([OH:24])=[O:23])[C:6]=1[C:17]([OH:19])=[O:18])[CH3:16]Diethyl 1,4-bis(ethyloxy)-2,3-naphthalenedicarboxylate (24.8 g, 68.8 mmol) was suspended in ethanol (200 ml) and treated with sodium hydroxide (8.3 g, 206.4 mmol) dissolved in 200 ml of water. A further 50 ml of ethanol added to aid stirring. Heated to reflux, 100° C. All in solution on heating. Refluxed for 8 hours. Cooled to room temperature and stood overnight. Solvent was evaporated to almost dryness. Water was added and stirred in an ice bath. Acidified with 2M HCl solution (˜150 ml). The white precipitate was filtered, washed with water and dried in a vacuum oven to give the title compound as a white solid (18.77 g, 61.7 mmol).
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