To sulfolane (10 mL) was added phosphoryl chloride (1.39 g, 9.05 mmol) at rt. Triethylamine (0.92 g, 9.05 mmol) was added dropwise with cooling. tert-Butyl 3-cyano-4-hydroxy-5,8-dihydrothieno[2,3-b:5,4-c′]dipyridine-7(6H)-carboxylate from Example 52A (1.00 g, 3.02 mol) was added, and the mixture was heated to 70° C. for 1.5 h. The mixture was cooled to rt, and triethylamine (2.3 mL) was added. A semi-saturated aqueous sodium chloride solution (10 L) was added whilst cooling with an ice-bath. The mixture was stirred at rt for 30 min and then extracted with ethyl acetate. The organic layer was washed with water, dried over sodium sulfate, and the solvent was removed in vacuo. Toluene was added, and the mixture was washed with water. The organic layer was again dried over sodium sulfate, and the solvent was removed in vacuo. After crystallization, the product was triturated with water, collected by suction filtration and dried to yield 543 mg (51%) of the title compound.
