ABSTRACT
The preparation of novel nucleoside analogues as antiviral and antitumor agents is critical for drug development. In addition to the modification of the sugar residue of nucleosides, there is increasing interest in C-nucleosides. Homonucleosides are a variation of C-nucleosides in which a methylene or alkylidene group is inserted between C-1 of the furanosyl moiety and the heterocycle. 1,2 C-C linkage of β-d-ribofuranosyl or 2-deoxy-β-d-erythro-pentofuranosyl to propene generates allyl C-glycosyl compounds, which are convenient precursors for the synthesis of homonucleosides. Therefore, there is interest in preparing these compounds stereoselectively on a gram-scale. In order to fix the furanose form, d-ribose was condensed with acetone to provide 2,3-O-isopropylidene-d-ribofuranose 2 3–5 (87%). Traces (ca. 0.4%) of 1,2:3,4-di-O-isopropylidene-α-d-ribopyranose 6,7 were removed by flash chromatography. Transformation of 2 into the diacetyl derivative 3 4 was achieved in 93% yield. The diacetate 3 was converted into the C-furanosyl compound 4 by treatment with allyltrimethylsilane (AllTMS) and zinc bromide in MeNO2 as solvent. 8–10 We were able to isolate the pure, protected β-C-furanosyl compound 4 in 78% yield from the reaction mixture (α/β ratio 1:6).
