Synthesis of 2′,3′-Didehydro-2′,3′-dideoxynucleosides Utilizing Coupling Reactions Between Nucleic Bases and Phenylthio-Substituted 2, 3-Dideoxyribose.

Stereoselectivities in coupling reactions between silylated pyrimidine bases and 3- or 2-α-phenylthio-2,3-dideoxyribose were examined. In the former case, no stereoselectivities were observed when the coupling reactions were performed either with 1-chlorosugar in an S N 2 mode or in the presence of Lewis acids as catalyst in an S N 1 mode. Coupling reaction with 2-α-phenylthio-2,3-dideoxyribose in the presence of Lewis acids, especially SnCl 4 , proceeded with good stereoselectivity to give anomeric mixtures of α:β=1:9. All these nucleosides were converted to 2',3'-didehydro-2',3'-dideoxynucleosides by oxidation to sulfoxides followed by thermal elimination of sulfenic acid