Metal-Graphite Reagents in Carbohydrate Chemistry. 8. The Scope and Limitations of the Use of Zinc/Silver-Graphite in the Synthesis of Carbohydrate-Derived Substituted Hex-5-enals and Pent-4-enals

Article abstract of DOI:10.1021/jo00006a047

The compatibility of different organic functional groups with the use of the zinc/silver-graphite reagent was investigated, utilizing 23 6-bromo-6-deoxy- or 6-deoxy-6-iodohexopyranosides and 5-deoxy-5-iodopentofuranose derivatives.These compounds possessed O-acetyl, O-benzoyl, O-methyl-, or O-p-tolylsulfonyl, O-benzyl, O-methyl, O-isopropylidene, epoxy, acetamido deoxy, azido deoxy, chloro deoxy, and deoxy fluoro groups and included a mono and a dideoxy derivative.Reductive dealkoxyhalogenation of these compounds gave, in most instances, a single product, a hex-5- or pent-4-enal, which could be considered a precursor for carbocyclization reactions.Iodides reacted faster than bromides, and pyranose derivatives reacted faster and more cleanly than furanose derivatives.The kinetic or thermodynamic stability of the product enal was found to be structure-dependent.Reduction of the carbon-halogen bond was one of the few side reactions observed.A mechanism for the reductive ring cleavage is proposed.