Copper‐Catalyzed Preparation of γ‐Alkylidenebutenolides and Isocoumarins under Mild Palladium‐Free Conditions

A general and efficient copper(I)‐catalyzed cross‐coupling and heterocyclization reaction of terminal alkynes and β‐iodo‐α,β‐unsaturated acid derivatives has been developed under very mild conditions. This method provides easy access from good to excellent yields of a variety of 5‐ylidenebutenolides and 3‐substituted isocoumarins with excellent regio‐ and stereoselectivity. This procedure does not require the use of any expensive supplementary additives, and is palladium‐free.