Methylenecyclohexenes: inversion barriers from the far-infrared spectra

Smithson, T. L.; Ibrahim, N.; Wieser, H.

doi:10.1139/v83-079

Cited by 11 publications

(5 citation statements)

References 8 publications

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“…For the preparation of 1 in quantity, the method of Blomquist et al involving the Prins reaction of cyclohexene and formaldehyde followed by flow pyrolysis of the resulting 3-acetoxymethylcyclohexene is preferred to the reaction of the Wittig reagent from methyl bromide with cyclohex-2-enone, or that from 3-bromocyclohexene with formaldehyde . Although yields are low in all procedures, the product of the flow pyrolysis can be purified by distillation (99%), whereas that from the other two methods requires laborious enrichment by preparative GLC to achieve no better than 90% purity. , …”

Section: Resultsmentioning

confidence: 99%

Thermal Reactions of anti- and syn-Dispiro[5.0.5.2]tetradeca-1,8-dienes: Stereomutation and Fragmentation to 3-Methylenecyclohexenes. Entropy-Dictated Product Ratios from Diradical Intermediates?

et al. 2001

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A series of cyclobutanes substituted 1,2- by polyenes of increasing radical-stabilizing power has been investigated to test the proposition that stabilization energies obtained independently from apposite, cis,trans geometric isomerizations can be successfully transferred to another system, in this paper, cyclobutanes. The first member of the series, 3-methylenecyclohexene (1), is photodimerized to anti- and syn-dispiro[5.0.5.2]tetradeca-1,8-dienes (anti-2 and syn-2), which undergo stereomutation (stereochemical interconversion) and cycloreversion (fragmentation) to 1 when heated in the range 72.1-118.2 degrees C: anti-2 --> syn-2, DeltaH() = 30.3 kcal mol(-)(1), DeltaS() = 0.2 cal mol(-)(1) K(-)(1); anti-2 --> 1, DeltaH() = 32.8 kcal mol(-)(1), DeltaS() = +8.0 cal mol(-)(1) K(-)(1). Agreement with an enthalpy of activation predicted by assuming full allylic stabilization in a hypothetical diradical intermediate is good. An example of further activation by a radical-stabilizing group is manifested by the approximately 20 000-fold acceleration in rate shown by the system 1-phenyl-3-methylenecyclohexene (3) and anti- and syn-2,9-diphenyldispiro[5.0.5.2]tetradeca-1,8-dienes (anti-4 and syn-4), measured, however, only at 43.6 degrees C. In both systems 2 and 4, volumes of activation for stereochemical interconversion and cycloreversion have been determined and found to be essentially identical within experimental uncertainties, DeltaV() = +10.2 +/- 1.0 and +12.6 +/- 1.4 cm(3) mol(-)(1), respectively (weighted means). These strongly positive values are consistent with the rate-determining step being the first bond-breaking, while the near identity of the volumes of activation argues against the indispensable second bond-breaking being a determining factor in fragmentation. These results are consistent with the theoretically based construct of Charles Doubleday for the paradigm, cyclobutane, in which the ratio between two channels of exit from a "generalized common biradical" is not controlled by enthalpy and entropy, as in the transition state model, but by entropy alone.

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Section: Resultsmentioning

confidence: 99%

Thermal Reactions of anti- and syn-Dispiro[5.0.5.2]tetradeca-1,8-dienes: Stereomutation and Fragmentation to 3-Methylenecyclohexenes. Entropy-Dictated Product Ratios from Diradical Intermediates?

et al. 2001

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“…All other common solvents and chemicals were used as received. 3-Methylenecyclohexene ( 5o ), 1-methyl-1,3-cyclohexadiene ( 5p ), and Pd 2 (dba) 3 ·CHCl 3 were prepared according to literature procedures.…”

Section: Methodsmentioning

confidence: 99%

Highly Regioselective Thiocarbonylation of Conjugated Dienes via Palladium-Catalyzed Three-Component Coupling Reactions

2000

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Three-component coupling reaction of conjugated dienes, thiols, and carbon monoxide affords an atom-economical thiocarbonylation of the dienes to give beta,gamma-unsaturated thioesters as the sole products. A catalyst system based on [Pd(OAc)(2)] and Ph(3)P showed excellent catalytic activity. The thiocarbonylation was performed under an atmosphere of carbon monoxide (400 psi) at 110 degrees C in CH(2)Cl(2) for 60 h. A wide variety of thioesters were synthesized in good to excellent yields from easily accessible starting materials. The reaction is believed to proceed via a eta(3)-allylpalladium intermediate. The thiocarbonylation, which is applicable to a wide variety of conjugated dienes, occurs in high regioselectivity, the latter dependent on the steric characteristics and stability of the eta(3)-allylpalladium complex.

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“…2E) have been reported in the region of 80-400 cm À1 , and interpreted with a view to identifying the two lowest out-of-plane deformations (inversion and twisted modes) of the cyclohexene ring [7]. Typical c-type band sequences are observed and interpreted in terms of ring inversion modes.…”

Section: Introductionmentioning

confidence: 74%

“…23579.18 0.03 9 (3, 7) ‹ 8 (3,6) 24269.25 0.03 9 (1, 8) ‹ 8 (1, 7) 24489.90 0.02 9 (2, 7) ‹ 8 (2,6) 25468.55 À0.11 10 (2, 9) ‹ 9 (2,8) 26068.42 0.00 11 (1, 11) ‹ 10 (1, 10) 26699.11 0.01 11 (0, 11) ‹ 10 (0, 10) 26755.47 À0.04 10 (9, 2) ‹ 9 (9, 1) 26853.00 0.00 10 (1, 9) ‹ 9 (1,8) 26874.91 0.00 10 (7, 4) ‹ 9 (7,3) 26892.82 0.08 10 (3, 8) ‹ 9 (3,7) 26939.75 0.06 10 (4, 7) ‹ 9 (4,6) 27067.83 0.17 10 (4, 6) ‹ 9 (4,5) 27169.61 À0.05 10 (3, 7) ‹ 9 (3,6) 27820 (3,9) 32197.54 À0.02 31186.32 0.02 12 (11, 1) ‹ 11 (11,0) 32220.36 À0.14 12 (10, 2) ‹ 11 (10,1) 32235.10 0.01 12 (9, 3) ‹ 11 (9,2) 32254.86 À0.01 31199.06 0.08 12 (8, 5) ‹ 11 (8,4) 32282.70 0.00 31223.16 0.02 12 (7, 6) ‹ 11 (7,5) 32324.00 0.25 31258.71 À0.01 12 (5, 8) ‹ 11 (5,7) 32486.85 À0.11 12 (5, 7) ‹ 11 (5,6) 32513.79 À0.12 31420.46 0.01 12 (4, 9) ‹ 11 (4,8) 32555.39 À0.06 12 (4, 8) ‹ 11 (4,7) 32901.88 0.09 13 (2, 12) ‹ 12 (2,11) 33360.70 À0.11 32404.63 À0.07 12 (2, 10) ‹ 11 (2,…”

Section: Fitted Structural Parameters and Comparison Of Those Of Relamentioning

confidence: 99%

Microwave spectrum, molecular structure, and theoretical calculation of anti-2-cyclohexen-1-one oxime

Aburatani

Sato

Yamamoto

et al. 2006

Journal of Molecular Spectroscopy

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Methylenecyclohexenes: inversion barriers from the far-infrared spectra

Cited by 11 publications

References 8 publications

Thermal Reactions of anti- and syn-Dispiro[5.0.5.2]tetradeca-1,8-dienes: Stereomutation and Fragmentation to 3-Methylenecyclohexenes. Entropy-Dictated Product Ratios from Diradical Intermediates?

Thermal Reactions of anti- and syn-Dispiro[5.0.5.2]tetradeca-1,8-dienes: Stereomutation and Fragmentation to 3-Methylenecyclohexenes. Entropy-Dictated Product Ratios from Diradical Intermediates?

Highly Regioselective Thiocarbonylation of Conjugated Dienes via Palladium-Catalyzed Three-Component Coupling Reactions

Microwave spectrum, molecular structure, and theoretical calculation of anti-2-cyclohexen-1-one oxime

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