4-{2-[5,6-bis(Benzyloxy)pyridazin-3-yl]ethynyl}oxan-4-ol (Intermediate 59; 2.0 g, 4.8 mmol) was dissolved in dichloromethane (20 ml). Triethylamine (2.94 g, 28.82 mmol, 6.0 equiv.) was added to the clear solution followed by the addition of methanesulfonyl chloride (1.64 g, 14.42 mmol, 3.0 equiv.) at room temperature. The reaction mixture was stirred for an hour at room temperature before the reaction mass was poured into water (200 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 to get the crude title compound (1.0 g, 52% yield) which was used as such for the next step without further purification.
