[C:1]([C:4]1[C:13]2[C:7]([CH:8]=[CH:9][C:10]([CH:14]([CH3:16])[CH3:15])=[CH:11][CH:12]=2)=[C:6]([CH2:17][CH3:18])[CH:5]=1)([OH:3])=[O:2].[C:19](Cl)(=O)[C:20](Cl)=O.C(O)C>C1C=CC=CC=1>[CH2:19]([O:2][C:1]([C:4]1[C:13]2[C:7]([CH:8]=[CH:9][C:10]([CH:14]([CH3:15])[CH3:16])=[CH:11][CH:12]=2)=[C:6]([CH2:17][CH3:18])[CH:5]=1)=[O:3])[CH3:20]The above-mentioned azulene carboxylic acid (3) (4.84 g, 0.002 mole) is suspended in benzene (100 ml), and oxalyl chloride (2.8 g, 0.02 mole) is added dropwise thereto under cooling with ice. The mixture is stirred for 3 hours at room temperature and cooled with ice again. Ethyl alcohol (100 ml) is added dropwise thereto and stirred for 2 hours at room temperature. The mixture is poured into ice-water (300 ml) and extracted with benzene (100 ml). The benzene layer is separated, and then washed with water. The benzene solution is concentrated under reduced pressure, and n-hexane is added thereto to obtain the ethyl ester derivative (2) at a yield of 4.5 g, 83.3%, having a melting point of 48° to 49° C.
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