Metal-Ligand Cooperation in the Cycloisomerization of Alkynoic Acids with Indenediide Palladium Pincer Complexes

Indenediide Pd complexes 1a-c are shown to very efficiently catalyze the cycloisomerization of alkynoic acids into alkylidene lactones via metal ligand cooperation (TON up to 2000). Complexes 1a-c are competent toward a broad range of alkynoic acids, including functionalized and internal ones, and give access to 5- as well as 6- and 7-membered lactones in excellent yields and with very high selectivities.