✍ Scribed by Yannick Landais; Liliana Parra-Rapado
No coin nor oath required. For personal study only.
Scheme 16 stereospecific mercury-desilylation of the cyclopropylmethylsilanes offers an entry to homoallylic derivatives which can be versatile synthons for organic synthesis. This was demonstrated through a short and stereoselective access to carba-sugars, to precursors of carba-nucleosides and to carba-C-disaccharides. The silicon group plays a central role in this context, controlling the diastereofacial selectivity of the cyclopropanation, the regio-and also the stereoselectivity of the cyclopropane ring opening. It is also worth noting the remarkable dichotomy between the silicon and the hydroxy groups, as indicated by the reversal of regioselectivity observed during the mercury-mediated cyclopropane ring opening. This was used to devise a stereocontrolled route to diastereomeric trisubstituted tetrahydrofurans.
General Remarks: 1 H-and 13 C-NMR spectra were recorded on a Bruker AC-250 FT ( 1 H: 250 MHz, 13 C: 62.9 MHz), Bruker WH-360 FT and ( 1 H: 360 MHz, 13 C: 90.55 MHz), Bruker ARX-400 FT ( 1 H: 400 MHz, 13 C: 100.6 MHz) using CDCl 3 as internal reference unless otherwise indicated. The chemical shifts (δ) and coupling constants (J) are expressed in ppm and Hz, respectively. Ϫ Gas chromatography was run on a Fisons Intruments, GC 8000 series. Ϫ IR spectra were recorded on a PerkinϪElmer 1710 spectrophotometer, on a PerkinϪElmer Paragon 500 FT-IR spectrophotometer or on a PerkinϪElmer Mattson Unicam 500 16PC FT-IR. Ϫ Mass spectra were recorded on a Nermag R10Ϫ10C, chemical ionization (CI) with NH 3 or Vacuum Generators micromass VG 70/70E and DS 11Ϫ250 and EI (70 eV); m/z (%). High resolution mass spectra were recorded on a FTICR mass spectrometer Bruker 4.7T BioApex II. Ϫ Specific rotations were recorded on a PerkinϪ Elmer 241 polarimeter. Ϫ Elemental analyses were performed by the I. Beetz laboratory, W-8640 Kronach (D). Ϫ Melting points were not corrected and were determined by using a Büchi Totolli apparatus. Kugelrohr distillations were carried out using a Büchi GKR-50 apparatus. Ϫ Merk silica gel 60 (70Ϫ230 mesh), (230Ϫ400 mesh ASTM) and Baker silica gel (0.063Ϫ0.200 mm) were used for flash chromatography. Slow additions were conducted using a Precidor apparatus. Ϫ CH 2 Cl 2 , Et 3 N, (iPr) 2 NH were distilled from CaH 2 . THF was distilled from potassium. Et 2 O, hexane and DME were distilled from sodium. Chlorosilanes were distilled from magnesium.
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