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

Abstract

. 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

13C magnetic resonance studies. 129. Homoenolization in the camphenilone system. Examination of some 7-substituted derivatives

“…There was no evidence of y-exchange at the cyclopropylmethylene sites in l c although such hydrogens may be expected to be more acidic than their alicyclic counterparts. This contrasts sharply with the results for 21, which exhibits deuterium incorporation at the less hindered of the two cyclopropylmethylene hydrogens, with k -8.7 x s-', i.e., at a rate comparable to that found for the endo-6-hydrogen in l c (17). This suggests that the carbonyl group in 21 enhances the acidity of the cyclopropylmethylene hydrogen due to the orientation of the threemembered ring relative to the carbonyl .rr system, which differs from that in l c .…”

“…For additional evidence that the 5 : 1 ratio of 1 b to 3b is the equilibrium mixture, two tubes containing a 1: 1 mixture of l b and 16 were heated at 200°C for 245 and 345 h. Under these conditions 16 is cleanly isomerized to 17 in 90% yield (10). The neutral 16 17 product in each case was the same, within experimental error, 42% ( l b ) , 8% ( 3 b ) , 5% (16), and 45% (17), which confirmed the initial results for l b 3b equilibration. Under the same conditions, a series of experiments with l c as the initial ketone gave a neutral product (>90% recovery) whose 13c spectra contained two sets of signals attributable to l c and 3c but the components of the mixture could not be separated by glc or tlc.…”

“…With the assumption that the hydrogenolysis of lc-d, to lb-d, did not alter the ' H distribution, approximate first-order rate constants for exchange at the various sites in l c were estimated and these data are collected in Fig. 1 together with those for l b , 19 (9), 20 (16), and 21 (17). From these results it is apparent that the rates of exchange at C-6 are comparable in l b , l c , and 19, with exo exchange favored.…”

13C nuclear magnetic resonance studies. 114. An examination of the [3.3.1.0] → [4.3.0.0] rearrangement via β-enolization and H/D exchange in tricyclic ketones

“…By analogy with 1 l and 3, one could envisage proton abstraction to occur from C-3 and C-9 in the endo isomer 5, constituting an intramolecular competition between y-and p-enolization, respectively, while a comparison of the behavior of the exo isomer 6 with that of the exo counterpart of 3 was of interest because of the some- 'For part 1 13 see ref. 5. what surprising H/D exchange results found for the latter (7). For this reason, the sites and stereoselectivity of proton abstraction in 5 and 6 were established by the requisite HID exchange experiments.…”

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

“…Decoupling at 6 3.75 collapsed the 2.60 pattern to an apparent 1:3:3:1 quartet without affecting the 3.00 absorption, while simultaneous irradiation of the latter pattern changed the 2.60 multiplet to a doublet of triplets without altering the carbinyl absorption at 3.75. On the basis of these data, we conclude that this ketone is exo-6-tert-butoxy-3,3-dimethylbicyclo[3.3.0]octan-2-one (15) and the I3c shieldings fit nicely upon comparison with those for 2 with due allowance for the effects of the 6-alkoxy substituent ( Table 1).…”