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8482551 
Journal Article 
Unusual Kinetic Stability of Enols to Ketonization: 1,2-Dimesityl-3-methylbut-1-en-1-ol and Related β-Alkyl-α,β-dimesitylethenos 
Nadler, EB; Rappoport, Z 
1990 
Yes 
Journal of Organic Chemistry
ISSN: 0022-3263
EISSN: 1520-6904 
55 
9 
2673-2682 
English 
The β-alky]-α,β-dimesitylethenols 3 and the isomeric β-alkyl-α,β-dimesitylethanones 4 (β-alkyl = Me, Et, i-Pr) were prepared and their spectral properties are reported. X-ray diffraction of the β-isopropyl enol 3d showed that the two mesityl rings are nearly perpendicular to the double-bond plane. Attempts to determine the 3/4 equilibrium constants in hexane were unsuccessful. Under no conditions were identical 3/4 mixtures obtained starting separately from the enol and ketone precursors. Under catalytic conditions the enols isomerized very slowly and the ketones did not isomerize at all, suggesting that the ketone is favored at equilibrium and that the slow and incomplete isomerization is due to the high kinetic stability of the enols. This is ascribed to the hindered approach of the acid catalysts to of the double bond of the enol or the enolate ion due to its shielding by the aryl groups and is corroborated by analysis of the occupied and empty space around the protonation site in 3d. © 1990, American Chemical Society. All rights reserved.