Ruthenium-catalyzed ring-closing metathesis: Recent advances, limitations and opportunities

Recent advances in ruthenium-catalyzed ring closing metathesis are discussed, in context of both substrate and catalyst parameters. As well as thermodynamic (substrate) constraints on ring-closing, root causes and effects of non-ideal catalytic performance are examined. Key substrate parameters are outlined, with a particular focus on the balance between oligomerization and ring-closing in RCM macrocyclization reactions. Advances in catalyst design are examined from a mechanistic viewpoint, including initiation requirements, catalyst deactivation, and opportunities resulting from incorporation of pseudohalide ligands. An overview of methods for reducing ruthenium residues in organic products to ppm levels is presented.