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1.1.5 Conclusions and Future Perspectives

DOI: 10.1055/sos-SD-221-00001

Gao, S.; Wang, D.Science of Synthesis: Metal-Catalyzed Cyclization Reactions, (2016150.

In summary, this chapter has presented palladium-, chromium-, copper-, and nickel-catalyzed or -promoted intramolecular coupling reactions for the formation of cyclic compounds with different ring sizes and functionalities. Despite considerable achievement in this field, much remains to be explored and optimized to enrich the toolbox of metal-catalyzed cyclic couplings. Instead of using the classical electrophilic and nucleophilic coupling components, the direct activation and functionalization of inert bonds, such as C—H and C—C bonds, provides novel strategies for C—C or C—X bond formations, which make such processes an essential part of current trends in metal-catalyzed reactions. Currently, this research topic is very active because of its significance in academic studies and the potential applications in pharmaceuticals. Reductive coupling of organic halides also holds the promise of extensive applications in organic synthesis, although it remains an immature method. Further studies in this field may focus on the discovery of new catalysts and ligands, which may decrease the dosage of reductants and enable a broader reaction scope in both inter- and intramolecular versions. For the chromium-mediated Nozaki–Hiyama–Kishi (NHK) coupling reactions, catalytic enantioselective coupling remains an unsolved challenge. We anticipate that explorations will continue to ensure that these methodologies and new discoveries will be powerful tools for preparing natural products and drug molecules.