Rates of Acid- and Base-Catalyzed Enolization of trans-Hexahydrofluorenone. Concerning Stereoelectronic Control of Enolization

Article abstract of DOI:10.1021/jo00195a021

Rates of both acid-catalyzed and base-catalyzed enolization of trans-hexahydrofluorenone (trans-HHF) have been measured and compared with those for a variety of other ketones.It was found that trans-HHF enolizes substantially faster than cyclohexyl phenyl ketone (CPK) in both acid (1800-fold) and base (2650-fold).This rate variation is thought to be due to two factors. (1) In trans-HHF the cleaving C-H bond is held rigidly parallel to the ? orbital of the ketone.About a factor of 25- to 60-fold is attributed to this stereoelectronic effect. (2) There are stericinteractions in the enol of CPK which decrease its rate of enolization by about 40- to 50-fold.