A mixture of POCl3 (0.79 ml) and N-methylformanilide (1.07 ml) was stirred at 22° C. for 10 min. To the solid formed was added a solution of 5-fluoro-1-naphthalen-1-ylmethyl-1H-indole-2-carboxylic acid ethyl ester (2.00 g from Example 15) in 1,2-dichloroethane (25 ml) and the solution was stirred at reflux temperature for 5 h. The solution was poured into a solution of ice-cold water (40 ml) containing sodium acetate (4.6 g) and stirring was continued at 22° for 2 h. The layers were separated, the aqueous layer extracted with dichloromethane, the combined extracts were dried, evaporated and the residue was chromatographed on silica using n-heptane/AcOEt (10:1) to give 5-fluoro-3-formyl-1-naphthalen-1-ylmethyl-1H-indole-2-carboxylic acid ethyl ester as a colorless solid. MS: 376.4 ([M+H]+).
