3,4-bis(Benzyloxy)-6-ethynylpyridazine (Intermediate 5; 3.0 g, 9.49 mmol) was dissolved in tetrahydrofuran (24 ml) under nitrogen atmosphere and the resulting solution was cooled to −78° C. n-Butyl lithium (23% solution in hexane; 7.92 ml, 28.48 mmol, 3.0 eq) was added slowly at −78° C., and the resulting mixture was allowed to stir for 30 minutes. Dihydro-2H-pyran-4(3H)-one (1.0 g, 10.44 mmol, 1.1 equiv.) was added slowly to reaction mass and the whole was allowed to warm to room temperature. The crude mixture was then poured into a saturated solution of aqueous ammonium chloride (300 ml) and product was extracted into ethyl acetate (100 ml×2). The organic layer was separated, washed with brine, dried (Na2SO4) and concentrated in vacuo. The crude product was purified by column chromatography on silica gel (eluting with 0-30% ethyl acetate in hexane) to yield the desired material (2.0 g, 501% yield).
