Abstract
The twelve isomeric gem-dimethylphenylvalerolactones may each in principle be
obtained by one of the general methods : (i) selective
reduction of the corresponding trisubstituted glutaric anhydride, (ii)
selective reduction of a gem-dimethyl-5-oxo-5-phenylvaleric acid, or (iii)
selective reaction of 2- or 3-phenylglutaric anhydride with 2 moles of
methylmagnesium iodide. ��� Substituted glutaric anhydrides for method
(i) were obtained by Michael addition of an
appropriate saturated ester to an appropriate α,β-unsaturated
ester, and reduced to the corresponding pairs of lactones. Two of the
intermediates for method (ii) may be obtained by Friedel-Crafts reaction of
2,2- or 3,3-dimethyl-glutaric anhydrides with benzene, but 4,4-dimethyl-5-oxo-5-phenylvaleric
acid is not produced in this way, and was obtained by an alternative method in
the literature. ��� Some of the required lactones were obtained
by variants of the general methods, and 5-t-butyl-3,3-dimethylvalerolactone
was prepared for comparison by reaction of 3,3-dimethylglutaric anhydride with
t- butylmagnesium chloride. The product lactones were structurally identified
from chemical shifts and the general nature of coupling patterns in their p.m.r. spectra, reinforced by values of geminal coupling
constants where available, and, in the case of 4,4-dimethyl-3- phenyl-valerolactone,
by results of nitration. Coupling constants obtained by iterative analyses of p.m.r. spectra for all but two of the lactones are
tabulated. Carbonyl-stretching frequencies for the solid state (or liquid
films) and for carbon tetrachloride solutions were also measured, and are
discussed.
Cited by
11 articles.
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