Practical synthesis of 4′-selenopyrimidine nucleosides using hypervalent iodine

We report herein a synthesis of 4′-selenouridine 12 and 4′-selenocytidine 14, substrates for the synthesis of 4′-selenoRNA. The Pummerer-like reaction between the selenoxide 9 and a silylated uracil afforded the desired 4′-selenouridine derivative 10; however, the chemical yield of 10 was rather low. In addition, the reproducibility of this reaction was poor because of the instability of the selenoxide 9. Improvement of this Pummerer-like reaction to give 10 was achieved when the 4-selenosugar 8 was treated with TMSOTf, 2,6-lutidine and the silylated uracil in the presence of iodosylbenzene.