On the Stereochemistry of Diaryl-Substituted Cyclohexanones Formed by Michael Reactions. Trans to Cis Isomerization of Their Ketals under Basic Conditions
作者:Alex T. Rowland、Sandra A. Filla、Marilyn L. Coutlangus、Mark D. Winemiller、Mark J. Chamberlin、Gary Czulada、Steven D. Johnson、Michal Sabat
DOI:10.1021/jo9801059
日期:1998.6.1
The stereochemistry of C-1-substituted 2,6-diphenylcyclohexan-4-ones 1-3 prepared by Michael reactions has been investigated. While preparations of these compounds have been reported over the past 70 years, in many instances the correct stereochemistry at C-2 (6) and, in some instances at C-1, was uncertain. We show here that in one case in which two identical substituents (CN) are present at C-1, it is possible to isomerize the initially formed trans isomer Id to the cis isomer 3f. When a cyano group and a dissimilar substituent are present at C-1, the initially formed trans isomer may be isomerized to the cis compound. The stereochemistry is vertified by NMR spectroscopy and by X-ray analysis. Reaction of the ethylene ketals (4 and 5) of these ketones with KOH in DMSO at elevated temperatures gives rise to cis products, and deuterium-labeling studies demonstrated the acidity of the benzylic hydrogen at C-2 (6). Isomerization was evident since the trans ketal 4a and the cis ketal 4b gave the same amide 6a. H-1 and C-13 NMR spectra provided conclusive evidence for the cis - trans rearrangement.