- Enantiomerically pure decalinic structures from carbohydrates using intramolecular Diels-Alder and Ferrier carbocyclization
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The synthesis of enantiomerically pure decalinic structures, advanced intermediates for the synthesis of the hexahvdronaphtalen part of mevinic acids, is described. The key steps are the intramolecular Diels-Alder cycloaddition of a suitably substituted sugar enone obtained via the Ferrier rearrangement of tri-O-acetyl-D-glucal with the appropriate alcohol representing the diene part of the system. Chemical manipulation of the resulting. diastereomerically pure, cycloadduct led to a 5,6-unsaturated carbohydrate which was submitted to the Ferrier carbocylization. This reaction proved difficult likely because of the embedding of the aglycon in a cycle, the hydration product of the double bond being the main product. This compound was in turn transformed into the decalinic structures by treatment in basic medium. The inverse strategy. Ferrier carbocyclization followed by IMDA of an enone and a diene linked via an ester bond was unsuccessful.
- Taillefumier, Claude,Chapleur, Yves
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p. 708 - 722
(2007/10/03)
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- The Reaction of Methyl 4,6-O-Isopropylidene-2,3-O-thiocarbonyl-α-D-mannoside with Methyl Iodide: a Synthesis of Methyl α-Tyveloside (Methyl 3,6-Dideoxy-α-D-arabino-hexopyranoside)
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The reaction of methyl 4,6-O-isopropylidene-2,3-O-thiocarbonyl-α-D-mannoside with methyl iodide gives two major products, methyl 3,6-dideoxy-3,6-diiodo-2-O-(methylthio)carbonyl-α-D-altropyranoside and methyl 2,3-O-carbonyl-6-deoxy-6-iodo-α-D-mannopyranoside, both of which lack the 4,6-O-isopropylidene grouping but contain the 6-deoxy-6-iodo function, and another minor product.One of the major product, methyl 3,6-dideoxy-3,6-diiodo-2-O-(methylthio)carbonyl-α-D-altropyranoside, is convertedinto methyl α-tyveloside by sequential reduction and ester removal.The incorporation of iodine at C 6 is seemingly due to hydrogen iodide, and may be suppressed in the presence of N,N,N,N-trtramethylnaphthalene-1,8-diamine or propylene oxide, or by the use of 4,6-O-benzylidene-2,3-O-thiocarbonyl-α-D-mannoside as substrate.Methyl iodide/propylene oxide is apparently an efficient combination for thiocarbonate (C=S) into carbonate conversion.The structure of the minor product was shown by single-crystal X-ray diffraction to be 1,6-anhydro-3-deoxy-3-iodo-2-O-(methylthio)carbonyl-β-D-altropyranose.
- Patroni, Joseph J.,Skelton, Brian W.,Stick, Robert V.,White, Allan H.
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p. 987 - 999
(2007/10/02)
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