Hydrochloric Acid → 3-Vinyl-phthalide

3.6 g of 7-[(4,6-dimethoxy-pyrimidin-2-yl)oxy]-3-hydroxyphthalide (see Example 84) are placed in 60 ml of absolute tetrahydrofuran at -45° C., and the solution is treated within 10 minutes with 18 ml of a 2M solution of vinylmagnesium chloride solution in tetrahydrofuran. The reaction solution is then stirred for approximately 16 hours at room temperature, a further 6 ml of vinylmagnesium chloride solution are added and the reaction solution is heated at reflux temperature for a further hour. When it has cooled, the reaction solution is acidified with 1N hydrochloric acid and freed of tetrahydrofuran in a rotary evaporator. The aqueous phase is then extracted with tert-butyl methyl ether, and the organic phase in washed and concentrated by evaporation under reduced pressure. Silica gel chromatography using ethyl acetate/n-hexane (2:3) as eluant yields pure 7-[4,6-dimethoxy-pyrimidin-2-yl)oxy]-3-vinyl-phthalide, m.p. 94°-97° C.