Chiroptical studies-part 99: The circular dichroism of seven-membered lactams and lactones |
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Authors: | W. Klyne D.N. Kirk J. Tilley H. Suginome |
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Affiliation: | Chemistry Department, Westfield College, Hampstead, London NW3 7ST, England;Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060, Japan. |
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Abstract: | This empirical analysis of CD data for 7-membered lactams includes examples of all twelve possible structural types in which the lactam is fused to a cyclohexane ring as part of a polycyclic compound. The CD behaviour of several classes of lactams shows ‘dOgura's sign rule’ to be an over-simplification. The signs and values of Δ? for lactams in which the second ring is fused at the 3,4- or 6,7-positions of the lactam ring show considerable deviations from the “normal’ values for 4,5- or 5,6-fused lactams.No simple pattern of group contributions emerged from this analysis, but a correlation of CD behaviour with the torsion angle in the C-CO-NH-C structural component is suggested, on the basis of a study of Dreiding models, and is supported by the result of an X-ray crystallographic analysis of one of the lactams.This study of CD data is extended to a smaller group of lactones with a seven-membered ring, most of which show Cotton effects opposite in sign and of smaller magnitude than those of the corresponding lactams. |
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