Organocatalytic Synthesis of Higher-Carbon Sugars: Efficient Protocol for the Synthesis of Natural Sedoheptulose and D-Glycero-L-galacto-oct-2-ulose

Herein we report a short and efficient protocol for the synthesis of naturally occurring higher-carbon sugars-sedoheptulose (D-altro-hept-2-ulose) and D-glycero-L-galacto-oct-2-ulosefrom readily available sugar aldehydes and dihydroxyacetone (DHA). The key step includes a diastereoselective organocatalytic syn-selective aldol reaction of DHA with D-erythrose and D-xylose, respectively. The methodology presented can be expanded to the synthesis of various higher sugars by means of syn-selective carbon-carbon-bond-forming aldol reactions promoted by primary-based organocatalysts. For example, this methodology provided useful access to D-glycero-D-galactooct-2-ulose and 1-deoxy-D-glycero-D-galacto-oct-2-ulose from D-arabinose in high yield (85 and 74%, respectively) and high stereoselectivity (99: 1).