Ring inversion in some fully α-methylated cycloalkane-1,2-diones

Variable-temperature NMR spectra of 3,5,5,5-tetramethylcyclopentane-1,2-dione (1a) and its 6-, 7- and 8-membered homologues (1b-d) showed conformational isomerization for the letter three compounds, the barrier to their ring inversion being 37.5, 38.9 and 62.7 kJ/mol, respectively.