[CH2:1]([SH:3])[CH3:2].C[OH:5].CC1C=CC(S([O:16][CH2:17][C@H:18]2[O:22][C@@H:21](OC)[C@@H:20]3OC(C)(C)O[C@H:19]23)(=O)=O)=CC=1>C[O-].[Na+]>[CH2:20]([CH2:19][C@@H:18]([OH:22])[C@@H:17]([OH:16])[C@@H:2]([OH:5])[CH:1]=[S:3])[CH3:21]A solution of ethanethiol (11.5 ml, 155 mmol) in 1N sodium methoxide in methanol (150 ml, 150 mmol sodium methoxide) was added to a solution of methyl 2,3-O-isopropylidene-5-O-p-toluenesulfonyl-β-D-ribofuranoside (50 g, 140 mmol in 200 ml dry methanol) and heated at reflux for 24 h. Solvents were removed by evaporation in vacuo, and the sticky residue was taken up in diethyl ether (300 ml) and washed with water (4×100 ml). The ether phase was dried and concentrated in vacuo to furnish a viscous oil. Fractional distillation (70° C. at 0.06 Torr) using a short-path distillation apparatus afforded 30.0 g (86.5% yield) of methyl 5-deoxy-5-ethylthio2,3-O-isopropylidene-β-D-ribofuranoside (III) as a colorless, viscous oil. TLC (silica; 25% ethylacetate in hexane): Rf 0.44 (III); visualization spray as in A above.
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