A solution of n-butyllithium (2.5M in hexanes, 22 mL) was added dropwise to a solution of 2-(pent-4-ynyloxy)tetrahydropyran (Intermediate 25, 7.70 g) in THF (60 mL), at −60° C. The mixture was stirred and allowed to warm to 15° C. over 1 hour. It was then re-cooled to −60° C. and a solution of tributyl tin chloride (16.4 g) in THF (50 mL) was added dropwise over 30 minutes. The mixture was stirred and allowed to warm to 20° C. over 1 hour. 1M aqueous sodium hydroxide (4 mL) was cautiously added and the resultant mixture was filtered through Celite, and washed with ethyl acetate. The filtrate was concentrated in vacuo and the residue was purified by chromatography on silica, eluting with a mixture of ethyl acetate and cyclohexane with a gradient of 0-100% to give tributyl-[5-(tetrahydropyran-2-yloxy)-pent-1-ynyl]-stannane (5.44 g).
