Synthesis of γ-Pyrones and N-Methyl-4-pyridones via the Au Nanoparticle-Catalyzed Cyclization of Skipped Diynones in the Presence of Water or Aqueous Methylamine

Supported Au nanoparticles on TiO2 catalyze the hydration/6-endo cyclization of skipped diynones to gamma-pyrones in aqueous dioxane, via triple bond activation. The isomeric 3(2H)-furanones which could be formed through a competing and often prevailing 5-exo cyclization pathway using homogeneous ionic Au(I) catalysts were not seen. The reaction does not proceed via the initial 1,3-transposition of the skipped diynones to their corresponding conjugated 1,3-diynone isomers. If aqueous methylamine is added, N-methyl-4-pyridones are exclusively formed in 69-79% yields via an analogous hydroamination/Au-catalyzed 6-endo cyclization pathway.

Automated summary

Au nanoparticles supported on TiO2 efficiently catalyze the hydration/6-endo cyclization of skipped diynones, leading to the formation of gamma-pyrones in aqueous dioxane. The reaction proceeds via triple bond activation, bypassing the formation of isomeric 3(2H)-furanones through a competing 5-exo cyclization pathway and the initial 1,3-transposition of the skipped diynones.