13C NMR spectral characterization of epimeric rotenone and some related tetrahydrobenzopyranofurobenzopyranones
The 13 C nuclear magnetic resonance (nmr) spectra of epimers of rotenone and four 12a-hydroxy-analogues were examined to determine the stereochemical effect of the B/C ring fusion involving the 6a- and 12a-carbon centers. Chemical shift differences between the epimeric carbon resonances of cis- and trans-6a,12a-compounds were notably larger than those of diastereoisomers derived from the same B/C ring junction stereochemistry. Results of the spectral analysis have been useful for the quantification of mixtures of epimers and for the measurement of rates of epimerization and oxygenation.
Journal of Heterocyclic Chemistry↗