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Under argon, 8-ethynyl-2,3,7,9,9-pentamethyl-1,4-dioxaspiro[4.5]dec-6-en-8-ol (500 mg, 1.99 mmol) was dissolved in a round-bottom flask in abs. dichloromethane (15 ml) and cooled to 0° C., and lutidine (0.58 ml, 4.99 mmol) and triethylsilyl trifluoromethanesulfonate (0.68 ml, 2.99 mmol) were added dropwise. The resulting reaction mixture was stirred at 0° C. for 1 h and at room temperature for a further hour, and water was added after the reaction had ended. The aqueous phase was repeatedly extracted thoroughly with dichloromethane, and the combined organic phases were then dried over magnesium sulfate, filtered and concentrated under reduced pressure. By final column chromatography purification of the resulting crude product (ethyl acetate/heptane gradient), [(8-ethynyl-2,3,7,9,9-pentamethyl-1,4-dioxaspiro[4.5]dec-6-en-8-yl)oxy](triethyl)silane (400 mg, 55% of theory) was obtained in the form of a colorless oil. 1H-NMR (400 MHz, CDCl3 δ, ppm) 5.30 (s, 1H), 4.20 (m, 1H), 3.58 (m, 1H), 2.48 (s, 1H), 2.02 (d, 1H), 1.86 (s, 3H), 1.79 (d, 1H), 1.22 (m, 3H), 1.14-0.93 (m, 9H), 0.75 (m, 6H), 0.53 (t, 9H). A multi-necked round-bottom flask which had been dried thoroughly by heating was flushed with argon and evacuated repeatedly, and zirconocene chloride hydride (311 mg, 1.21 mmol) and degassed abs. tetrahydrofuran (3 ml) were then added under a constant stream of argon. The reaction solution was cooled to 0° C., and a solution of [(8-ethynyl-2,3,7,9,9-pentamethyl-1,4-dioxaspiro[4.5]dec-6-en-8-yl)oxy](triethyl)silane in abs. tetrahydrofuran (2 ml) was added dropwise. The resulting reaction solution was stirred at room temperature for 1 h and its analysis by NMR spectroscopy showed complete conversion into the desired biscyclopentadienyldimethyl[(E)-2-{2,3,7,9,9-pentamethyl-8-[(triethylsilyl)oxy]-1,4-dioxaspiro[4.5]dec-6-en-8-yl}vinyl]zirconium. 1H-NMR (400 MHz, CDCl3 δ, ppm) 7.75 (m, 4H), 7.36 (m, 6H), 7.27 (d, 1H), 5.39 (d, 1H), 5.31 (s, 1H), 3.69 (m, 1H), 3.62 (m, 1H), 2.10-2.06 (m, 2H), 1.61 (s, 3H), 1.32-1.22 (m, 12H), 0.89 (m, 6H), 0.83 (t, 9H). The synthesis intermediate II.25 obtained in this manner was used in the subsequent reaction in question without further purification.

1. customThe resulting reaction mixture
2. extractionThe aqueous phase was repeatedly extracted thoroughly with dichloromethane
3. dry with materialthe combined organic phases were then dried over magnesium sulfate
4. filtrationfiltered
5. concentrationconcentrated under reduced pressure
6. customBy final column chromatography purification of the resulting crude product (ethyl acetate/heptane gradient)