**4. Future perspectives**

This review introduces the field of canbon-11 radiochemistry through a general overview, but is not meant to be comprehensive. As the field is fast growing, more traditional chemists join the radiochemistry arena worldwide. Carbon-11, one of the most important radioisotopes in nuclear medicine, is foreseen to have endless opportunities for further innovation. Due to the short half-life, efficiency and simplicity is always the key to 11C-labeling techniques. Recently developed transition-metal-mediated reactions have broadened the labeling scope and allowed 11C-labeling of a range of different bioactive molecules.

11C-chemistry is a hybrid science between organic chemistry and engineering. To meet the growing demand and increasing regulation of radiopharmaceuticals, the fully automated or kit-like synthetic devices have been developed and will be required to be used in the manufacture of clinical doses to improve the reliability and safety.

Furthermore, synthetic pathways with better economical output and environmental management is another important aspect. The first example of a green radiochemistry laboratory at University of Michigan successfully prepared 11 radiopharmaceuticals for routine clinical application using ethanol as the only organic solvent [105]. The removal of all other organic solvents from the process simplifies production and quality control testing. The robust and reliable methods are increasingly applied in various PET facilities around the world.
