ABSTRACT
Unsaturated carbohydrates, especially glycals (1,4-or 1,5-anhydro-2-deoxy-hex-or hept-1-enitols) and exo-glycals (2,5-or 2,6-anhydro-1-deoxy-hex-or hept-1-enitols), play an important role in getting a better insight into the action of carbohydrate derivatives in living organisms. They themselves are glycomimetics and offer many synthetic possibilities for further transformations. The synthesis1,2 and synthetic uses3 of glycals and exo-glycals4,5 are well documented and reviewed.6 Exomethylene glycals are relatively easily available in the ether-or silyl-protected series.4,7 Since such glycals are normally prepared at highly basic conditions and/or with the aid of organometallic reagents, O-acyl-protected derivatives are not so readily accessible due to the incompatibility of ester protecting groups at such reaction conditions. Herein, the direct synthesis of O-acyl-protected exo-glycals from (C-glycopyranosyl)formaldehyde tosylhydrazones is described.8,9
Melting points were measured in open capillary tubes or on a Ko—er hot stage and are uncorrected. Optical rotations were determined with a Perkin-Elmer 241 polarimeter at room temperature. Nuclear magnetic resonance (NMR) spectra were recorded with Bruker 360 (360/90 MHz for 1H/13C) or Bruker 400 (400/100 MHz for 1H/13C) spectrometers. Chemical shifts are referenced to internal TMS (1H) or to the residual solvent signals (13C). Proton chemical shifts and scalar coupling constants were extracted from the resolution-enhanced 1D proton spectra. Microanalyses were performed on a Carlo-Erba analyzer Type 1106. Thin-layer chromatography (TLC) was performed on DC-Alurolle Kieselgel 60 F254 (Merck), and the plates were visualized under UV light and/or by gentle heating. For column chromatography, Kieselgel 60 (Merck, particle size 0.063-0.200 mm) was used. Organic solutions were dried over anhydrous MgSO4 and concentrated under diminished pressure at 40-50°C (water bath).
