A Facile Preparation of the Ethylene Glycol Mono-Ketal of Cyclohexane-1, 4-Dione

The ethylene glycol mono-ketal of cyclohexane-1,4-dione (4) is an exceedingly useful bifunctional synthetic intermediate. In order to prepare synthetically useful amounts of the previously reported 1 pyrrolidine enamine 5, we have developed a straightforward route which starts from cyclohexane-1,4-diol (1). We have found that oxidation of diol 1 with slightly less than 1 equivalent of Jones reagent2 gives a mixture which contains a 90% yield of the desired hydroxy-ketone 2.3 The ketal 3 could be prepared directly from the crude hydroxy-ketone 2 by the standard procedure employing ethylene glycol and benzene with minimal extractive work up. We utilize a chromium trioxide-pyridine oxidation4 of the alcohol 3 to obtain the ketone-ketal 4. This procedure circumvents the problem caused by the high water solubility of intermediates 2 and 3 which frustrate some of the previously reported preparations.