Palladium‐Catalyzed Decarbonylative Iodination of Aryl Carboxylic Acids Enabled by Ligand‐Assisted Halide Exchange

We report an efficient and broadly applicable palladium‐catalyzed iodination of inexpensive and abundant aryl and vinyl carboxylic acids via in situ activation to the acid chloride and formation of a phosphonium salt. The use of 1‐iodobutane as iodide source in combination with a base and a deoxychlorinating reagent gives access to a wide range of aryl and vinyl iodides under Pd/Xantphos catalysis, including complex drug‐like scaffolds. Stoichiometric experiments and kinetic analysis suggest a unique mechanism involving C−P reductive elimination to form the Xantphos phosphonium chloride, which subsequently initiates an unusual halogen exchange by outer sphere nucleophilic substitution.