A mixture of triethylsilane (2.7 g), trifluoroacetic acid (1.6 g) and dichloroethane (8.0 mL) at −20° C. was treated dropwise with a mixture of (5-chloro-2-methylindol-1-yl)acetic acid methyl ester (0.36 g), 3-phenylsulphony-2-thiophenealdehyde (0.39 g) and dichloroethane (8.0 mL), and the resulting mixture was warmed to room temperature over a period of 1.5 hours. The mixture was treated with additional triethylsilane (2.7 g) and trifluoroacetic acid (1.6 g) and then stirred at room temperature for 1 hour. The mixture was diluted with saturated aqueous sodium hydrogen carbonate solution and extracted with dichloromethane. The combined organic extract was washed with saturated aqueous sodium chloride solution, dried over sodium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel, eluting with a mixture of dichloromethane and ethyl acetate (1:0 to 0:1 by volume) to afford the title compound (0.55 g).
