Rhodium‐Catalyzed Annulation of Glycals With Alkynes via C–H Activation: Synthesis of Pyridone‐ and Pyranone‐Fused Sugar Derivatives

Rhodium(III)‐catalyzed C–H activation/annulation reactions of glycal derivatives with alkynes have been developed, providing an efficient approach to structurally diverse pyridone‐ and pyranone‐fused sugar frameworks. The catalytic system of [Cp*RhCl 2 ] 2 /Ag 2 CO 3 in 1,2‐dichloroethane effectively promoted the annulation to give the pyridone‐fused product. The methodology was applicable to a wide range of glycal‐derived primary and secondary amides as well as carboxylic acids, affording the corresponding annulated sugars in moderate to excellent yields. Remarkably, the carboxylic acid‐based annulation proceeded under mild conditions (40°C–80°C) to give pyranone‐fused derivatives in high yields. The annulated products underwent smooth acidic deprotection to furnish the corresponding triols without decomposition, demonstrating the robustness of the fused heterocyclic frameworks.