The reaction of 2,4‐bis‐ O ‐trimethylsilyluracil (2) and 5‐fluoro‐2,4‐bis‐ O ‐trimethylsilyluracil (3), respectively, with acetals 4a – m of various aliphatic and aromatic aldehydes in the presence of trimethylsilyl trifluoromethanesulfonate (5) at ‐ 30°C gives the 1‐(1'‐alkoxyalkyl)‐ and 1‐(1'‐alkoxy‐1'‐phenylmethyl)‐pyrimidines 6a – m and the corresponding 5‐fluorouracil derivatives 7a – f in 40 – 91% yield.