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Determining C‐7 stereochemistry in C‐7‐substituted 6α,14α‐ endo ‐ethano‐ and 6α, 14α‐ endo ‐ethenotetrahydrothebaines by 13 C NMR; a re‐analysis
Author(s) -
Mazza Samuel M.
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310505
Subject(s) - chemistry , steric effects , chemical shift , stereochemistry , carbon 13 nmr
Abstract A re‐analysis of previously published 13 C NMR data on C‐7‐substituted 6α,14α‐ endo ‐ethanotetrahydrothebaines shows that the 13 C chemical shift of C‐18 in these medicinally important compounds can be used as an indicator of C‐7 stereochemistry, this being due to a steric gamma effect between C‐18 and C‐7 substituents in an α orientation. In seven examples of α‐isomers the C‐18 chemical shift ranges from δ17.02 to δ18.42 (average δ17.72), whereas in four examples of β‐isomers the C‐18 chemical shift ranges from δ22.09 to δ24.00 (average δ22.73‐23.40). Since suitable etheno compounds can be chemically reduced to ethano compounds, C‐7 stereochemistry in such 6α,14α‐ endo ‐etheno compounds can be determined indirectly.