Synthesis of Pyranones: Ru-Catalyzed Cascade Reaction via Vinylic C-H Addition to Glyoxylate.

The efficient synthesis of pyranones is presented by a three-component cascade reaction from readily available acrylic acids, ethyl glyoxylate, and p -toluenesulfonamide under ruthenium catalysis. For the first time, the nucleophilic addition of the vinylic C-H bond of acrylic acids across aldehyde is achieved, and the intramolecular cyclization as well as subsequent second insertion to aldehyde form the substituted butenolides. The elimination of sulfonamides occurs at higher temperature to give the pyranones.