Trifluoromethanesulfonic anhydride (3 ml, 15 mmol) was added to a dichloromethane (50 ml) solution of the obtained 6-decyl-3-methylthio-2-hydroxynaphthalene (3.63 g, 10 mmol) and pyridine (2.5 ml, 30 mmol) at 0° C. This solution was stirred at room temperature for 25 minutes. Then, the mixture was diluted with water (20 ml), and hydrochloric acid (4 M, 20 ml) was added. The mixture was extracted with dichloromethane (30 ml×3). The organic phases obtained by repeating the extraction three times were collected, washed with saturated saline water (30 ml×3), dried with MgSO4, and condensed to obtain 6-decyl-3-methylthio-2-(trifluoromethanesulfonyloxy)naphthalene (compound (4)-81) (4.89 g, 99%).
