Nuclear Magnetic Resonance Studies. XXVII. Homoenolization of Fenchone. A Mechanistic Study Utilizing C And H Nuclear Magnetic Resonance

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. J. Chem. 62, 1385Chem. 62, (1984.The effect of strongly basic conditions (t-BuOL/t-BuOH/I85"C) on the exo and endo isomers of 7,7-dimethyltricyclo[3.2. I .02."]octan-6-one has been examined. While the exo isomer is stable, the endo isomer readily rearranges to 4,4-dimethyltricyclo[3.3.0.0'.H]octan-3-one (6) which subsequently undergoes reduction of the three-mcrnbered ring. 'The initial transformation is one of very few examples of y-enolate rearrangement. Experiments in tert-butyl alcohol-0-d, were carried out to establish the several sites of deuterium incorporation in the initial ketones and in 6 using '~m r . These results reveal the stereochemistry of y-enolate formation and cleavage as well as the stercoselectivities and relative rates of the exchange processes.A. K. CHENG, ASHIM K. GHOSH et J. B. STOTHERS. Can. J. Chem. 62, 1385 (1984.On a CtudiC I'effet de conditions fortement basiques (t-BuO-/t-BuOH/l85"C) sur les isomeres exo et endo de la dimkthyl-7,7 tricyclo

Section: Hid Exchange Experimentssupporting

confidence: 66%

Nuclear magnetic resonance studies. XL. Tricyclooctanone rearrangement, [3.2.1.0] → [3.3.0.0], via γ-enolization and a ²Hmr study of H/D exchange in tricyclic ketones

Cheng¹,

Ghosh²,

Stothers³

1984

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“…Subsequently, a variety of mono-and bicy-ring-expanded product was not detected (2) indiclicketones,eachhavinggem-dimethylsubstitution cating that 2 4 3 is a minor process in t-BuO-/ at the a-methylene positions, has been found to t-BuOH at 185°C. Analogous results were found for exhibit a-methyl HID exchange in deuteriated base the other examples and, in all cases, the recovery of under homoenolization conditions (3)(4)(5)(6)(7). These starting material and/or rearranged products arisexamples include the tetramethylcycloalkanones ing through homoenolization at skeletal carbons was high.…”

supporting

confidence: 77%

Evidence for cyclopropoxide intermediates in α-methyl H/D exchange of cyclic ketones under homoenolization conditions

Patel¹,

Stothers²

1980

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“…Consequently a series of measurements at 155°C was performed to permit an improved assessment of t h e relative rates at the different sites in ketones 1-3. Deuterium incorporation was monitored by examination of the 'Hmr spectra of the deuterated products (4). Analysis of the proton spectra of 1-3 aided by the use of the Eu(fod), shift reagent and spin decoupling allowed unambiguous assign~nents of the signals in the 'H spectra.…”

mentioning

confidence: 99%

Nuclear magnetic resonance studies. XXXII. Rearrangement, isomerization, and deuterium exchange via β-enolization in bicyclooctenones. A ²H nuclear magnetic resonance study

Cheng¹,

Stothers²

1978

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A. K. CHENG and J. B. STOTHERS. Can. J. Chenl. 56, 1342Chenl. 56, (1978. The equilibration of the a,a-dimethyl derivatives of bicyclo[2.2.2]octenone, bicyclo[3.2.1]-oct-2-en-6-one, and its A3 isomer has been examined at 155 and 185°C in tert-BuO-lte1.t-BuOH. Using 'Hmr spectroscopy the rates and stereoselectivity of hydrogen-deuterium exchange in each of these ketones have been determined for equilibrations with tc,rt-BuOD as solvent. The relative reactivities for exchange at the allylic and vinylic sites compared to the analogous results for the corresponding olefins reveal a significant activating effect of the carbonyl group. Comparison of the data with those for the corresponding saturated ketones shows that the double bond enhances the rate of isomerization appreciably and increases the bias of the equilibrium toward the [3. Our earlier examinations of bicyclooctanones in strongly basic media had shown that the [2.2.2] and [3.2. I] skeletons are interconvertible and that the rate of isomerization is enhanced significantly in the unsaturated derivatives (1). We had found that the a,a-dimethyl derivatives of bicyclo[2.2.2]octenone (I), bicyclo[3.2. Iloct-2-en-6-one (2), and its A3 isomer 3 are equilibrated at 185°C in tert-butoxide -tertbutyl alcohol much more readily than their saturated analogs. From experiments in deuterated solvent it was found that hydrogen-deuterium exchange occurred at five carbon sites in 1-3 by examination of their 13Cmr spectra (In). These sites were C-2, -3, -4, -5, and the exo-methyl in 2 and 3. Exchange at C-4 and the methyl site occur by P-enolization whereas that at C-2 (and C-4) involves an allylic carbanion and that at C-3 a vinyl anion presumably. For 1 exchange occurred at C-1, -5, -6, -7, and the exo-methyl sites. It was of interest t o determine the relative rates of exchange at these sites and to examine the stereoselectivity at the methylene positions. A comparison of these data with the results of our examination of hydrogen-deuterium exchange in bicyclo[2. tene and bicyclo[3.2.1]oct-2-ene (2) would reveal a n activating effect of the carbonyl group on the reactivity of the allylic and vinyl anions in these skeletons. T o this end we have followed the progress of deuterium incorporation into ketones 1-3 as a function of time and determined the rates of isomerization using each of the three ketones a s starting material. Experiments were carried out at 155 and 185°C. A t the higher temperature, the data are directly comparable to the results obtained for a variety of ketonic substrates (3) but for some of the rate processes only lower li~nits could be estimated. Consequently a series of measurements at 155°C was performed to permit an improved assessment of t h e relative rates at the different sites in ketones 1-3. Deuterium incorporation was monitored by examination of the 'Hmr spectra of the deuterated products (4). Analysis of the proton spectra of 1-3 aided by the use of the Eu(fod), shift reagent and spin decoupling allowed unambiguous assign~nents of the signal...