Synthesis of Fluorinated Pyrones

Significance

A one-pot Sonogashira coupling-lactonization of cis-2,3-difluoro-3-iodo acrylic acid with terminal alkynes to give 3,4-difluoro-6-substituted-2-pyrones is reported. Aliphatic, heterocyclic and aromatic alkynes participate in this reaction to give pyrones in modest to good yields. Although electron-withdrawing and -donating groups on the aromatic acetylenes showed little effect on yields (e.g., CF₃, 69%; OMe, 71%), the yield of the pyridyl (43%) was compromised. An X-ray crystallographic structural analysis of the trifluorophenyl derivative was determined. A mechanism containing two catalytic cycles was proposed for the transformation.