The structures of the title compounds, bearing five-, six-, seven-, or eight-membered rings, have been investigated by u.v. and 1H n.m.r. spectroscopy. In the 4-oxo derivatives the enol-enamine-imine tautomerism depends greatly on the ring size, whereas in the 2-oxo series the enamine tautomer always predominates, independently of the ring size. In the 4-oxo series the five-membered homologues are mainly in the enol form, and the six-membered ones in the enamine form. The seven-membered derivative (21) exists as a mixture of the enamine and imine tautomers. In the eight-membered homologue (22) the imine form is preferred. The enol tautomer of the five-membered 4-oxo derivatives has the Z-configuration in chloroform, and the E-configuration in dioxane, whereas in ethanol and dimethyl sulphoxide E-Z isomeric mixtures are present, with concentration-dependent isomer ratios.
|Number of pages||7|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - Dec 1 1985|
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