The structures of five cyclic diketones isolated from coffee

Five cyclic diketones isolated from coffee oil (four of them isomeric) have been proved to be: (a) 3-methylcyclopentane-1,2-dione; (b) 3,4-dimethylcyclopentane-1,2-dione; (c) 3,5-dimethylcyclopentane-1,2-dione; (d) 3-ethylcyclopentane-1,2-dione; (e) 3-methylcyclohexane-1,2-dione. The structures of these compounds, postulated exclusively on the basis of spectroscopic data (U.V. I.R. and mass spectrometry), were confirmed by synthesis.