Efficient Synthesis of 2′-Bromo-2′-Deoxy-3′,5′-O-TPDS-pyrimidine Nucleosides by Boron Trifluoride Catalyzed Reaction of O2,2′-Anhydro-(1-β-D-Arabinofuran0Syl)pyrimidine Nucleosides with Lithium Bromide

Efficient syntheses of 2′-bromo-2′-deoxy-3′,5′-O-TPDS-uridine (5a) and 1-(2-bromo-3,5-O-TPDS-β-D-ribofuranosyl)thymine (5b) from uridine and 1-(β-D-ribofuranosyl)thymine are described, respectively. The key step is a treatment of 3′,5′-O-TPDS-O2,2′-anhydro-1-(β-D-ardbinofuranosyl)uracil (4a) and -thymine (4b) with LiBr in the presence of BF3-OEt2 in 1,4-dioxane at 60°C to give 5a and 5b in 98%, and 96% yield, respectively. 1. Partial Protection of Carbohydrate Derivatives. Part 30. For Part 29, see Kawashima, E; Aoyama, Y.; Sekine, T.; Miyahara, M.; Radowan, M. F.; Nakamura, E.; Kainosho, M.: Kyogoku, Y.; Ishido, Y.I. Org. Chem. submitted. #This paper is dedicated to Dr. Yoshihisa Mizuno, an Emeritus Professor of Hokkaido University, on the occasion of his 75th birthday.