Low Catalyst Loading in Ring-Closing Metathesis Reactions

• Published in: Chemistry : a European journal Vol. 19; no. 3; pp. 1002 - 1012
• Main Author: Kadyrov, Renat
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 14-01-2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Amides; Catalysts; Chemistry; Conversion; Decomposition reactions; heterocycles; Heterocyclic compounds; Lactones; macrocycles; Metathesis; ring closure; ruthenium; Synthesis
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201202207

An efficient procedure is described for ring‐closing metathesis reactions. A conversion of 95 % for diethyl diallylmalonate in dilute solution could be achieved within a few minutes, reaching TOF=4173 min−1, with very low loading of commercially available Ru catalysts that contained unsaturated NHC ligands. In general, only 50 to 250 ppm of the catalyst is required to achieve near‐quantitative conversion into a broad variety of 5–16‐membered heterocyclic compounds. The practicality of this procedure was illustrated in the synthesis of 5–8‐membered N‐tert‐butoxycarbonyl (N‐Boc)‐ and N‐para‐toluenesulfonyl (N‐Ts)‐protected cyclic amines and 9–16‐membered lactones. The synthesis of macrocyclic proline‐based lactams required slightly higher catalyst loadings. Along with monocyclic products, oligomeric byproducts, mostly cyclodimers, were isolated and characterized.
Getting some closure: An efficient procedure is described for ring‐closing metathesis reactions in which only 50 to 250 ppm of catalyst is required to effect almost‐quantitative conversion into a broad range of 5–16‐membered heterocyclic compounds. The practicality of this procedure was illustrated in the synthesis of 5–8‐membered N‐protected cyclic amines, 9–16‐membered lactones, and 11–16‐membered proline‐based lactams.