Homoenolization of 1,3,3-trimethylbicyclo[2.2.1]heptan-2-one in perdeuterated tert-butyl alcohol. Evidence that the medium potassium tert-butoxide – tert-butyl alcohol is unstable at elevated temperatures

Abstract

, 526 (1985). Homoenolization of I ,3,3-trimethylbicyclo[2.2. Ilheptan-2-one (1) (fenchone) in potassium tert-butoxide -tert-butyl alcohol-0-d and perdeuterated potassium tert-butoxide -tert-butyl alcohol at 220°C established that there is significant deterioration of the medium and dilution of the deuterium pool. We show that the major pathway of deterioration of the medium and dilution of the pool involves formation of isobutene by elimination of water from the alcohol. Exchange data already accumulated in the literature are used to support our view that the elimination also occurs at 185"C, the temperature commonly used to homoenolize ketones.NICK HENRY WERSTIUK et GEORGE TIMMINS. Can. J . Chem. 63, 526 (1985). L'homoCnolisation, ti 220"C, de la trimethyl-1,2,3 bicyclol2.2. Ilheptanone-2 (1) (fenchone) en presence de tert-butylate de potassium/tert-butanol 0-d ou de tert-butylate de potassium/tert-butanol perdeutkre montre qu'il se produit une deterioration importante du milieu et une dilution de la quantite de deutkrium. Nous dkmontrons que la voie principale de la dkterioration du milieu et de la dilution de la quantitC de deutCrium implique une elimination d'eau de I'alcool conduisant a de I'isobutkne. On a utilisC les donnkes d'Cchange deja accumulCes dans la IittCrature pour appuyer notre conclusion selon laquelle I'Climination se produit Cgalement a 185OC, la tempkrature couramment utilises pour provoquer I'homoenolisation des cetones.[Traduit par le journal] Introduction Potassium tert-butoxide in tert-butyl alcohol-0-d has been used routinely to study hydrogen isotope exchange of carbon acids at elevated temperatures ( 1 , 2). In fact, it has been the medium of choice for homoenolizing ketones (3-5). Although it was suggested by Cram et al. that alkoxide bases react with glass (6) during exchange reactions at elevated temperatures, and recycling has been used by Nickon, Stothers, and coworkers in homoenolization studies (7,8) to increase deuterium incorporation, no definitive information was available as regards the stability of t-BuOK -t-BuOH(D) solutions. In this paper we show, through homoenolization of 1,3,3-trimethylbicyclo[2.2. I lheptan-2-one (fenchone) (1) at 220°C, that the solution definitely is unstable at elevated temperatures, determine the major pathway of its deterioration, and establish that perdeuterated rerr-butyl alcohol should be used as a solvent to improve the stability of the medium and maximize deuterium incorporation.