Monitoring ring-closing metathesis: Limitations on the utility of 1H NMR analysis

The utility and limitations of H-1 NMR methods for monitoring the progress of ring-closing metathesis (RCM) reactions are examined. H-1 NMR analysis of RCM reactions that yield macrocyclic and medium-ring products can be more problematic than is generally recognized. Interpretation is complicated by the formation of oligomers with an NMR signature identical or closely similar to that of the diene precursor, the RCM target, or a composite of the two. DOSY-NMR can aid in resolving ambiguities in signal assignment, but reliable quantitation requires ancillary methods. (C) 2009 Elsevier B. V. All rights reserved.