To a solution of 1-benzenesulfonyl-5-methylthioindole (0.5178 g) in tetrahydrofuran (17 ml), n-butyl lithium (1.3 ml, 1.59 M) was added dropwise at −78° C. and the mixture was stirred for 30 minutes, followed by addition of the compound obtained in Example 30 (1) (0.3444 g), and the mixture was stirred at −50° C. for 40 minutes. The reaction solution was poured into a saturated aqueous ammonium chloride solution and extracted with ethyl acetate. The organic layer was washed with a saturated aqueous NaCl solution, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The resulting residue was separated using silica gel column chromatography (hexane:ethyl acetate=1:1) to obtain 0.593 g of the desired product.
