Equilibrium between homocub-1(9)-ene and homocub-9-ylidene

Chen, Ning; Jones, Maitland; White, W. R.; Platz, Matthew S.

doi:10.1021/ja00013a038

Cited by 63 publications

(37 citation statements)

References 0 publications

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“…3 kcal mol -1 , our (2/2)CAS-SDCI/6-31G* calculations give n n G = -0 . 1 kcal mol -1 , in excellent agreement with the experimental results of Platz, Jones and co-workers [5].…”

Section: Resultssupporting

confidence: 90%

“…However, even the highest level calculations that we have performed give relative energies for the TS which are substantially above the value of E a = 5 kcal mol -1 , estimated from the kinetic data published by Platz, Jones and co-workers [5]. Possible reasons for this apparent disagreement between the calculations and the experiments on the rate of equilibration of 1b and 2b are discussed.…”

Section: Introductioncontrasting

confidence: 64%

“…5 kcal mol -1 higher in energy than 1b. Clearly, this value is in very poor agreement with the estimate of E a < 5 kcal mol -1 , derived from the experimental data of Platz and Jones [5].…”

Section: Introductioncontrasting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

“…The best studied example of the latter process was discovered by Eaton and Ho mann in the rearrangement of 9-phenylhomocub-1(9)-ene (1a) to 1-phenylhomocub-9-ylidene (2a) [3]. Subsequent investigations in the desphenyl series demonstrated that the parent ole® n (1b) also can be formed from the carbene (2b) [4], and experiments by Jones, Platz and coworkers have found the equilibrium constant for this reaction to be approximately unity at room temperature [5].Jones, Platz, and coworkers started with di erent precursors, which led initially either to 1b or to 2b. Independent of the precursor used, the same mixture of CH 3 OD trapping products of 1b and 2b was formed, provided that the concentration of CH 3 OD was less than 1 m. Therefore, under these conditions equilibration of 1b and 2b appears to be faster than trapping with CH 3 OD.…”

mentioning

confidence: 99%

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Ab initio calculations on the interconversion of homocub-1(9)-ene and homocub-9-ylidene

Hrovat¹,

Borden²

1997

Molecular Physics

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Calculations which include dynamic electron correlation beyond the CASSCF level have been carried out for the interconversion of homocub-1(9)-ene (1) and homocub-9-ylidene (2). The geometry of the transition state was also located at the (4/4)CASSCF/6-31G* level and was found to di er signi® cantly from the previously published (2/2)CASSCF/3-21G geometry. In agreement with experiment, calculations at the (2/2)CASSDCI+ Q/6-31G* level ® nd 1 and 2 to have free energies at 298 K that di er by only~0 . 1 kcal mol -1 . However, the activation energy for the rearrangement of 1 to 2 of E a = 12 . 9 kcal mol -1 , computed at this level of theory, is considerably higher than the experimental estimate of E a < 5 kcal mol -1 . Additional calculations in which the size of the basis set was increased or in which the active space was expanded to 4 electrons in 4 orbitals suggest that the calculated E a may be reduced to as low as 8 kcal mol -1 . However, there is no indication that higher level calculations would give a value of E a as low as 5 kcal mol -1 . Possible reasons for this apparent disagreement between the calculations and the experiments on the rate of equilibration of 1 and 2 are discussed. IntroductionRearrangements of carbenes to ole® ns usually are irreversible reactions [1]. Nevertheless, bridgehead ole-® ns with su cient torsional strain are capable of undergoing reversion to carbenes [2]. The best studied example of the latter process was discovered by Eaton and Ho mann in the rearrangement of 9-phenylhomocub-1(9)-ene (1a) to 1-phenylhomocub-9-ylidene (2a) [3]. Subsequent investigations in the desphenyl series demonstrated that the parent ole® n (1b) also can be formed from the carbene (2b) [4], and experiments by Jones, Platz and coworkers have found the equilibrium constant for this reaction to be approximately unity at room temperature [5].Jones, Platz, and coworkers started with di erent precursors, which led initially either to 1b or to 2b. Independent of the precursor used, the same mixture of CH 3 OD trapping products of 1b and 2b was formed, provided that the concentration of CH 3 OD was less than 1 m. Therefore, under these conditions equilibration of 1b and 2b appears to be faster than trapping with CH 3 OD.Flash photolysis studies indicated that both the ole® n and carbene react with CH 3 OD within an order of magnitude of the di usion controlled rate. Taken together, these two observations indicate that the rate constant for equilibration of 1b and 2b at room temperature

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“…3 kcal mol -1 , our (2/2)CAS-SDCI/6-31G* calculations give n n G = -0 . 1 kcal mol -1 , in excellent agreement with the experimental results of Platz, Jones and co-workers [5].…”

Section: Resultssupporting

confidence: 90%

Section: Introductioncontrasting

confidence: 64%

“…5 kcal mol -1 higher in energy than 1b. Clearly, this value is in very poor agreement with the estimate of E a < 5 kcal mol -1 , derived from the experimental data of Platz and Jones [5].…”

Section: Introductioncontrasting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Ab initio calculations on the interconversion of homocub-1(9)-ene and homocub-9-ylidene

Hrovat¹,

Borden²

1997

Molecular Physics

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Reactive Intermediates fromN-Aziridinylimines

Kirmse

1998

Eur. J. Org. Chem.

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N‐Aziridinylimines are readily obtained from carbonyl compounds and 1‐aminoaziridines, of which the 2‐phenyl and trans‐2,3‐diphenylaziridine derivatives are the most popular. Diazo compounds are formed upon thermolysis or photolysis of N‐aziridinylimines, with elimination of alkenes. The diazo compounds can be trapped by intramolecular addition to alkenes, but otherwise decompose as they are formed, giving rise to carbenes and products derived therefrom. The transformation R2CO → R2CN2 → R2C is most often achieved with the anions (salts) of arenesulfonylhydrazones. However, the non‐ionic and weakly basic N‐aziridinylimines have the advantage that they are compatible with nonpolar solvents and with a wide range of substituents. These properties were exploited in the fragmentations of α,β‐epoxyketones (→ alkynones) and α,β‐epoxyaldehydes (→ β‐hydroxyvinylidenes → cyclopentenols) as well as in the syntheses of unsaturated nitriles, silanes, and ethers. Laser flash photolysis of N‐aziridinylimines in fluorinated alcohols was used to demonstrate the protonation of carbenes and to measure absolute reaction rates of carbocations. The Shapiro reaction of N‐aziridinylimines, performed with catalytic amounts of R2NLi, was found to produce alkenes with excellent regio‐ and stereoselectivity. As radical acceptors, N‐aziridinylimines are superior to alkenes. On this basis, selective (tandem) cyclizations were designed for the synthesis of natural products.

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