Remote C–H bond functionalization reveals the distance-dependent isotope effect

Iodination of remote aryl C–H bonds has been achieved using palladium acetate as the catalyst and iodoacetate (IOAc) as the oxidant. Systematic kinetic isotope studies imply a mechanistic regime shift as the number of bonds separating the directing heteroatom and the target C–H bond increases. Both isotope and electronic effects observed in remote C–H bond activation are consistent with an electrophilic palladation pathway in which the initial palladation is slower than the C–H bond cleavage.