Then, the lithium salt of the resulting thieno[2,3-b]pyridine-5-carboxylic acid, C-(5-phenoxy-thiophen-2-yl)-methylamine described in Preparation Example 26 (4.7 mg, 23 μmol), benzotriazol-1-yl-tris(dimethylamino)phosphonium hexafluorophosphate (14 mg, 32 μmol) and triethylamine (9 μl, 63 μmol) were dissolved in N,N-dimethylformamide (0.5 mL), and the solution was stirred at room temperature for 2 hours. Water and ethyl acetate were added to the reaction solution, the organic layer was partitioned, and washed with brine. The solvent was evaporated in vacuo, the residue was purified by silica gel column chromatography (hexane:ethyl acetate=1:1), and the title compound (3.0 mg, 8.2 μmol, 40%) was obtained as a white solid.
