Wasserstoffübertragungen, 10. Der cis‐selektive, zweistufige Wasserstoff‐Transfer von 1,4‐Dihydroarenen auf o‐ und p‐Chinone

Brock, M.; Hintze, H.; Heesing, Albert

doi:10.1002/cber.19861191218

Cited by 14 publications

(3 citation statements)

References 11 publications

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“…Related orders of hydride abstraction rates from the dihydroarenes 3 , 4 , and 5 (Tables and ) have also been found in their reactions with other hydride acceptors (Table ). It should be noted, however, that for the reactions of dihydroarenes with quinones the possibility of concerted didehydrogenation with direct formation of arenes has been discussed. ,− …”

Section: Discussionmentioning

confidence: 99%

Reactions of Carbocations with Unsaturated Hydrocarbons: Electrophilic Alkylation or Hydride Abstraction?

2002

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Benzhydryl cations were used as reference electrophiles to determine the hydride donor reactivities of unsaturated hydrocarbons. The kinetics of the reactions were followed by UV-vis spectroscopy and conductivity measurements, and it was found that the second-order rate constants for the hydride transfer processes were almost independent of the solvents or counterions employed. The rate constants correlate linearly with the previously published empirical electrophilicity parameters E of the benzhydrylium ions. Therefore, the linear free energy relationship log k(20 degrees C) = s(E + N) could be employed to characterize the hydride reactivities of the hydrocarbons by the nucleophilicity parameters N and s. The similarity of the slopes s for hydride donors and pi-nucleophiles allows a direct comparison of the reactivities of these different functional groups based on their nucleophilicity parameters N. Since nucleophilicity parameters of -5 < N < 0 have been found for a large variety of allylic and bisallylic hydride donors, a rule of thumb is derived that hydride transfer processes may compete with carbon-carbon bond-forming reactions when carbocations are combined with olefins of pi-nucleophilicity N < 0.

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Section: Discussionmentioning

confidence: 99%

Reactions of Carbocations with Unsaturated Hydrocarbons: Electrophilic Alkylation or Hydride Abstraction?

2002

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“…Independent support for this conclusion comes from an investigation of the kinetic isotope effect observed in the DDQ oxidation of the tetralin derivatives 9/9-1,1,4,4-D 4 and 9-D 12 . Heesing et al [34] have carefully studied the stereochemical course and the kinetic isotope effects for the oxidation of 1,2-dihydronaphthalene (7) and 1,3-cyclohexadiene (28) with the deuterated derivatives shown in Scheme 5 and various quinones such as 1 a and 10. The oxidation of cis-and trans-7-1,2-D 2 and À28-5,6-D 2 proceeds with 90 % and 98 % cis stereoselectivity, respectively.…”

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confidence: 99%

The Effect of Pressure on Hydrogen Transfer Reactions with Quinones

Wurche

Sicking

Sustmann

et al. 2004

Chemistry A European J

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The effect of pressure on the oxidation of hydroarenes 3-9 with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ; 1 a) or o-chloranil (10), leading to the corresponding arenes, has been investigated. The activation volumes were determined from the pressure dependence of the rate constants of these reactions monitored by on-line UV/Vis spectroscopic measurements in an optical high-pressure cell (up to 3500 bar). The finding that they are highly negative and only moderately dependent on the solvent polarity (DeltaV( not equal ) = -13 to -25 in MTBE and -15 to -29 cm(3) mol(-1) in MeCN/AcOEt, 1:1) rules out the formation of ionic species in the rate-determining step and is good evidence for a hydrogen atom transfer mechanism leading to a pair of radicals in the rate-determining step, as was also suggested by kinetic measurements, studies of kinetic isotope effects, and spin-trapping experiments. The strong pressure dependence of the kinetic deuterium isotope effect for the reaction of 9,10-dihydroanthracene 5/5-9,9,10,10-D(4) with DDQ (1 a) can be attributed to a tunneling component in the hydrogen transfer. In the case of formal 1,3-dienes and enes possessing two vicinal C--H bonds, which have to be cleaved during the dehydrogenation, a pericyclic hydrogen transfer has to considered as one mechanistic alternative. The comparison of the kinetic deuterium isotope effects determined for the oxidation of tetralin 9/9-1,1,4,4-D(4)/9-2,2,3,3-D(4)/9-D(12) either with DDQ (1 a) or with thymoquinone 1 c indicates that the reaction with DDQ (1 a) proceeds in a stepwise manner through hydrogen atom transfer, analogously to the oxidations of 1,4-dihydroarenes, whereas the reaction with thymoquinone 1 c is concerted, following the course of a pericyclic hydrogen transfer. The difference in the mechanistic courses of these two reactions may be explained by the effect of the CN and Cl substituents in 1 a, which stabilize a radical intermediate better than the alkyl groups in 1 c. The mechanistic conclusions are substantiated by DFT calculations.

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“…Several mechanistic pathways for the oxidation of benzylic C-H bonds with DDQ have been proposed, and these mechanisms have been investigated by a number of groups. [42][43][44][45][46][47][48][49] Detailed studies by Linstead, Jackman, and co-workers [50][51][52][53] concluded that most DDQ oxidations occur through a ratedetermining hydride transfer, leading to a delocalized carbocation which rapidly loses a proton or is trapped by a nucleophile. This mechanism is supported by ab initio calculations on the oxidation of cyclohexa-1,4-diene with DDQ that predicts an ionic mechanism in which an initial hydride transfer occurs.…”

Section: Resultsmentioning

confidence: 99%