Iridium-Catalyzed Cycloisomerization of Alkynoic Acids: Synthesis of Unsaturated Lactones

The iridium-catalyzed cycloisomerization of various alkynoic acids was successfully developed, and a series of five-, six-, and especially seven-membered unsaturated lactones were constructed with moderate yields and excellent regioselectivities (up to 68% yield, >99:1 rr). In addition, the indole compound can be easily prepared with 75% yield through this efficient synthetic methodology. Moreover, a plausible mechanism for this Ir-catalyzed cycloisomerization of alkynoic acids was proposed.