Catalytic Substitution Reactions for the Introduction of Hydrogen, Carbon, Fluorine and Iodine Isotopes

Abstract This perspective examines catalytic strategies for late-stage isotope incorporation into complex molecules, with an emphasis on hydrogen, carbon, and halogen isotope exchange and substitution reactions relevant to pharmaceutical, radiochemical, and analytical applications. It highlights how transition-metal catalysis, photoredox catalysis, electrochemistry, and heterogeneous or biocatalytic platforms enable selective isotopic labeling at advanced synthetic stages, while systematically assessing their scope, operational practicality, scalability, isotope economy, and remaining limitations. By connecting mechanistic innovation with applied requirements such as high isotopic incorporation, minimal radioactive waste, robust substrate tolerance, and transferability from deuterium to tritium or radiocarbon labeling, the article frames catalytic isotope chemistry as an enabling technology for ADME studies, PET imaging, quantitative bioanalysis, metabolic tracing, and isotopically optimized drug design. Isotope incorporation should be evaluated not only as a labeling problem but as an applied catalysis challenge. For catalytic isotope methods to become routine in pharmaceutical and radiochemical workflows, they must combine predictable selectivity, broad substrate tolerance, safe and efficient isotope handling, low catalyst and isotope loading, compatibility with complex molecules, and demonstrable scalability. This applied framework guides the comparison of hydrogen, carbon, and heteroatom isotope exchange methods throughout the article.