ON THE STEREOCHEMISTRY OF DIARYL-SUBSTITUTED CYCLOHEXANONES FORMED BYMICHAEL REACTIONS - TRANS TO CIS ISOMERIZATION OF THEIR KETALS UNDER BASIC CONDITIONS

The stereochemistry of C-1-substituted 2,6-diphenylcyclohexan-4-ones 1 -3 prepared by Michael reactions has been investigated. While preparat ions of these compounds have been reported over the past 70 years, in many instances the correct stereochemistry at C-2 (6) and, in some ins tances at C-1, was uncertain. We show here that in one case in which t wo identical substituents (CN) are present at C-1, it is possible to i somerize the initially formed trans isomer Id to the cis isomer 3f. Wh en a cyano group and a dissimilar substituent are present at C-1, the initially formed trans isomer may be isomerized to the cis compound. T he stereochemistry is vertified by NMR spectroscopy and by X-ray analy sis. Reaction of the ethylene ketals (4 and 5) of these ketones with K OH in DMSO at elevated temperatures gives rise to cis products, and de uterium-labeling studies demonstrated the acidity of the benzylic hydr ogen at C-2 (6). Isomerization was evident since the trans ketal 4a an d the cis ketal 4b gave the same amide 6a. H-1 and C-13 NMR spectra pr ovided conclusive evidence for the cis - trans rearrangement.