Neighboring-Group Participation. The Preparation of Dithiopentose Sugars via a Thioacylonium Ion Intermediate¹

Stereoselective Synthesis and Antiviral Activity of d-2‘,3‘-Didehydro-2‘,3‘-dideoxy-2‘-fluoro-4‘-thionucleosides

“…To confirm which carbon center has epimerized, the hydroxyl methyl ester 3a was subjected to reclosure of the ring to give the starting 2-fluorobutenolide 3 under basic conditions (Scheme 2). The spectroscopic data ( 1 H and 13 C NMR) of this compound matched that of the starting compound, which suggested that there was no significant epimerization during saponification followed by methylation. Iodination under several different reaction conditions, however, confirmed that high temperature and longer reaction time resulted in partial To achieve a clean and high-yield conversion, the temperature of the reaction mixture had to be carefully controlled in such a manner that, after addition of TMSOTf at 0 °C, the reaction mixture was stirred for 6 h at room temperature and then for 2 h at 60 °C.…”

“…Melting points were determined on a Mel-temp II apparatus and are uncorrected. Nuclear magnetic resonance spectra were recorded on a Bruker 400 AMX spectrometer at 400 MHz for 1 H NMR and 100 MHz for 13 C NMR with tetramethylsilane as the internal standard. Chemical shifts (δ) are reported as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), or br s (broad singlet).…”

“…The crude thiolactol was treated with Ac 2O (19 mL) and DMSO (20 mL) at room temperature for 24 h. The reaction mixture was poured to a separatory funnel containing ice-cooled water (300 mL) and extracted with ethyl ether (3 × 300 mL). The combined organic layer was washed with water (3 × 300 mL), dried over MgSO 4, filtered, concentrated, and purified by silica gel column chromatography with 5% Et 2O in hexanes to give the product 6 (4.2 g, 10.8 mmol, 54% yield) and 6a (0.7 g, 1.8 mmol, 9% yield) as yellow oil: For 6: [R] 25 D 28.2°(c 1.08, CHCl3); 1 H NMR (CDCl3) δ 7.68-7.37 (m, 10H), 5.07 (ddd, J ) 50.5, 10.2, 6.9 Hz, 1H), 3.96-3.78 (m, 3H), 2.70-2.62 (m, 1H), 2.18-2.05 (m, 1H), 1.07 (s, 9H); 13 (2R,4S)-(+)-4-tert-Butyldiphenylsilyloxymethyl-2-fluoro-2-phenylselenyl-γ-thiobutyrolactone (7). To a solution of compound 6 (4.74 g, 12.2 mmol) in THF (60 mL) was added 14.7 mL of 1 M LiHMDS in THF slowly at -78 °C, and the reaction mixture was stirred at the same temperature for 1 h. TMSCl (2.01 mL, 15.9 mmol) was added dropwise to the reaction mixture, and the mixture was allowed to warm to room temperature.…”

“…The first example of 4‘-thionucleosides was reported in 1964 by Reist et al, who synthesized the 4‘-thio counterpart of naturally occurring adenosine . Since then, several classes of 4‘-thionucleosides have been reported, including 9-(4-thio- d -xylofuranosyl)adenine, 9-(4-thio- d -arabinofuranosyl)adenine, and 4‘-thio-araC . However, the difficulty of synthesizing optically pure 4‘-thionucleosides has impaired additional syntheses of these analogues, and only a few examples have been known until recently .…”

Chemistry of apiose. VI. Influence of reaction conditions and stereochemistry on some thioacetate displacemtnes with carbohydrate sulfonates

“…Anal. Caled for Ci6H2608S2: C, 46.81; H, 6.38; S, 15.62. Found: C, 46.82; H, 6.38; S, 15.44. To a solution of 2 in water (ca.…”