Metal-mediated decarbonylation and dehydration of ketose sugars

Article abstract of DOI:10.1021/om00113a029

Ketose sugars can be decarbonylated and/or dehydrated by the action of certain metal complexes. Fructose reacts with 1 equiv of RhCl(PPh₃)₃ (1) in N-methyl-2-pyrrolidinone (NMP) at 130°C to give furfuryl alcohol, Rh(CO)Cl(PPh₃)₂ (2), and a small amount of 1-deoxyerythritol. 1,3-Dihydroxyacetone consumes 2 equiv of 1, giving methane and ca. 2 mol of 2. With manno-2-heptulose the primary product is 2,7-anhydromanno-2-heptulopyranose. The mechanisms of these unusual reactions have been studied by using ¹³C-labeling experiments and model reactions employing Pd(II) and HCl. Attempts to make the reactions catalytic using [Rh(Ph₂PCH₂CH₂CH₂PPh ₂)₂]⁺[BF₄]^- in place of 1 were not successful. The use of NMP as a solvent offers some advantages in the acid-catalyzed synthesis of certain carbohydrate dehydration products, as exemplified by the conversion of manno-2-heptulose to its 2,7-anhydride and of 2-deoxyglucose to 1-(2-furanyl)-1,2-ethanediol.