.beta.-Epimerization and .gamma.-hydrogen abstraction via homoenolate ions

supporting

confidence: 78%

mentioning

confidence: 99%

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

Patel¹,

Stothers²

1980

“…Very few examples of y-enolization have been encountered and, heretofore, only one has been found to lead to skeletal rearrangement, namely, the isomerization of half-cage ketone 1 to 2 (3). The formation of y-enolates has been inferred from the observation of HID exchange at C-8, the syn-methyl carbon, of camphor (4), at C-6 and -7 in 3,3-dimethylbicyclo[3.3.0]octan-2-one (5), and at the endo-6-methyl carbon of 3,3,6,6-tetramethyl[2.2.l]heptan-2-one (6). The conversion of symtetramethyldiphenylacetone to 2-isopropyl benzoic acid (7) can be viewed formally as rearrangement through a y-enolate, but specific activation of proton abstraction from the phenyl ring by the carbonyl group seems unlikely and the process cannot be taken as a true example of y-enolization within the usual frame of reference.…”

Section: Introductionmentioning

confidence: 99%

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

. 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

“…Upon formation of the monocyclic ester(s), equilibration of the A2' and A3' isomers can occur readily in the strongly basic medium via allylic anions. It has been shown previously that tert-butyl esters from such ketonic cleavages do not survive the reaction conditions and are isolated as the corresponding carboxylic acids (16). Since the samples of 5-d, recovered from the experiments in deuterated base lacked detectable deuterium at C-8, proton abstraction from this site must be irreversible such that opening of the resulting p-enolate leads only to 6 a .…”

Section: Discussionmentioning

confidence: 97%

¹³C magnetic resonance studies. 131. An examination of β-enolization in an unsaturated [3.2.1] system: 3,3-dimethylbicyclo[3.2.1]oct-6-en-2-one

Antoniadis¹,

Clements²,

Peiris³

et al. 1987

. 65, 1557 (1987).Under homoenolization conditions (I-BuO-/I-BuOH/ 185"C), 3,3-dimethylbicyclo[3.2.l]oct-6-en-2-one (5) is converted into six products through three reaction pathways. The major product, 3,3-dimethylbicyclo[3.3.0]octan-2-one, arises by unidirectional p-enolate rearrangement of 5 to the isomeric unsaturated [3.3.0] ketones, which (a) undergo efficient reduction to 2, by single electron transfer, and (b) suffer Haller-Bauer cleavage to two isomeric 2,2-dimethyl-3-cyclopentenylpropanoic acids. In competition with these processes is the reversible conjugate addition of I-BuO-to 5 to furnish the 6-tert-butoxy derivative, which undergoes p-enolate rearrangement to two isomeric ketones. The structures of these products were established primarily from their ' H and I3C magnetic resonance spectra.GREG A. ANTONIADIS, MICHAEL T. M. CLEMENTS, SRIYAWATHIE PEIRIS et J. B. STOTHERS. Can. J. Chem. 65, 1557.Dans des conditions d'homoCnolisation (I-BuO-/I-BuOH/185"C), la dimethyl-3,3 bicyclo[3.2.1]octkne-6 one-2 (5) se transforme en six produits, par le biais de trois voies rCactionnelles. Le produit principal, la dimethyl-3,3 bicyclo[3.3.0]octanone-2, provient d'une transposition unidirectionnelle du p-Cnolate du compost 5 en cetones [3.3.0] insaturees isomkres (a) qui subissent une reduction efficace en 2 par un transfert unique d'electron et (b) qui subissent un clivage de Haller-Bauer pour conduire a deux acides dimethyl-2,2 cyclopentkne-3 yl propanoi'ques isomkres. Ces processus sont en competition avec ['addition conjuguee reversible de l'anion I-BuO-au compose 5 qui conduit au derive tert-butylate-6 qui subit une transposition P-Cnolique conduisant i deux cetones isomkres. Pour determiner les structures, on a principalement fait appel aux spectres de resonance magnetique nucltaire du 'H et du I3c.[Traduit par la revue]