Copper Catalyzed Atom Transfer Radical Cyclization Reactions

Atom transfer radical cyclization (ATRC) is a powerful technique to prepare functionalized 4-10 membered ring systems using transition metal catalysts. In this review recent advances in the use of copper complexes are described. In particular the effect of different ligands on reactivity, selectivity and product outcome are illustrated with application to heterocycle and natural product synthesis. New approaches that increase catalyst efficiency with supplemental reducing agents are reviewed and examples using green solvents, benign reducing agents (e.g. ascorbic acid) and with catalyst loadings as low as 0.05 mol-% are highlighted. Radical addition to aromatic rings and rearrangement reactions under ATRC conditions as well as application to radical-polar crossover reactions are also described.