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

The utility and limitations of 1H NMR methods for monitoring the progress of ring-closing metathesis (RCM) reactions are examined. 1H 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.

Graphical abstractConventional 1-D NMR spectroscopy can be misleading in reporting on reaction rates and yields in the RCM synthesis of macrocyclic and medium-ring targets. DOSY-NMR can aid in resolving ambiguities in the assignment of signals due to the starting dienes, the RCM targets, and oligomeric intermediates.Figure optionsDownload full-size imageDownload as PowerPoint slide