Effect of pressure on the [2 + 2 .fwdarw. 4] cycloaddition reaction of tetracyanoethylene to enol ethers

Jouanne, Joern Von; Kelm, H.; Huisgen, Rolf

doi:10.1021/ja00495a026

Cited by 39 publications

(10 citation statements)

References 11 publications

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“…For example, the activation volume of the [ ). [19] Similar results were obtained for the alkylation of pyridine with benzyl bromide (DV°= À29.2 cm 3 mol À1 in acetonitrile and DV°= À39.1 cm 3 mol À1 in toluene). [18] To distinguish between the mechanistic alternatives of the quinone dehydrogenation-the direct hydride transfer leading to a pair of ions (comparable to the intermediary zwitterion in the polar [2 + 2] cycloaddition) and the hydrogen atom transfer leading to a pair of non-charged radicals (Scheme 1: mechanisms (1) and (2), respectively)-we determined the activation volumes of the reactions of DDQ (1 a) with the hydroarenes 3±9 and of o-chloranil (10) with 5 and 6 in MTBE (tert-butyl methyl ether: E T = 34.7, e = 4.5 D) and in the more polar mixture (1:1) of acetonitrile (E T = 45.6, e = 35.5 D) and ethyl acetate (E T = 38.1, e = 6.0 D) as solvents.…”

Section: Introductionsupporting

confidence: 70%

“…Thus, the overall effect, called electrostriction, leads to negative volumes of activation and reaction. [17] In associative formation of ions-in the alkylation of pyridine derivatives (Menshutkin reaction) [18] or in the polar [2 + 2] cycloaddition of a vinyl ether to tetracyanoethylene (TCNE), [19] for example-both effects are volume-contracting and sum to give highly negative volumes of activation and reaction, which are strongly dependent on the solvent polarity. In nonpolar solvents the volume contraction caused by the effect of electrostriction is larger than in polar solvents.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionsupporting

confidence: 70%

Section: Introductionmentioning

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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“…It is known that the formation of dipolar intermediates from neutral cycloadducts is stimulated by high pressure. [2] Dipolar ring-opening becomes increasingly facile with increasing stabilization of the positive charge by the alkoxy group, which explains the presence of the cyclobutane at room temperature in the case of tert-butoxyethene. Scheme 3 The cyclobutanes are more stable against dipolar ringopening than the dihydropyrans, and as a consequence of this are also more stable against acid-catalyzed solvolysis.…”

Section: Cycloaddition Reactions Of 2-cyano-3-aryl-2-propenoates Withmentioning

confidence: 99%

“…[1,2] In a preceding paper we showed that enol ethers react smoothly under high pressure conditions with a large variety of 1,1-dicyanoalkenes giving rise to a large variety of 1,1-dicyanocyclobutanes. [3] The reaction has a broad scope, allowing the introduction of substituents at every position of the cyclobutane skeleton.…”

Section: Introductionmentioning

confidence: 99%

High-Pressure Promoted Cycloadditions of Enol Ethers and 3-Aryl-2-cyano-2-propenoates

2002

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The high-pressure promoted cycloadditions of enol ethers (1) and alkyl 3-aryl-2-cyano-2-propenoates (2) lead stereoselectively in high yields to 2,6-dialkoxy-4-aryl-3,4-dihydro-2H-pyran-5-carbonitriles (3). These cycloadducts have a high potential for further synthesis due to the presence of various functionalities. This is illustrated with some representative conversions. As reactive cyclic ketene acetals the cycloadducts 3 were easily hydrolyzed to aldehydes (6) or ketones or alcoholized to acetals having additional ester and cyano

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“…The [2+2] cycloaddition of tetracyanoethene (TCNE) to vinylethers shows a powerful pressure-induced acceleration resulting in highly negative activation volumes (for example ∆V ≠ = -55.0 cm 3 mol -1 , ∆V = -31.9 cm 3 mol -1 (25 °C, CH 2 Cl 2 ) for the cycloaddition [83]. Detailed mechanistic studies [84] allow the conclusion that these reactions proceed stepwisely passing through interceptable dipolar intermediates.…”

Section: ____________________________________________________________mentioning

confidence: 99%

The Effect of Pressure on Organic Reactions

Klärner¹,

Wurche²

2000

J. prakt. Chem.

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The utility of high pressure for the understanding of chemical reactions and its application in organic synthesis is shown for cycloadditions (inter‐ and intramolecular Diels‐Alder reactions, 1,3‐dipolar and [2+2] cycloadditions), cheletropic reactions and pericyclic rearrangements (Cope and Claisen rearrangements and electrocyclizations). The origin of the effect of pressure on chemical reactions is discussed. Especially, the change in the packing coefficient during cyclization of chains and the effect of electrostriction on reactions, in which charged species are generated, contribute substantially to a volume contraction leading to a powerful pressure‐induced acceleration of such reactions. Finally, the effect of pressure on free‐radical reactions (homolytic bond dissociations and quinone oxidations) is described.

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Effect of pressure on the [2 + 2 .fwdarw. 4] cycloaddition reaction of tetracyanoethylene to enol ethers

Cited by 39 publications

References 11 publications

The Effect of Pressure on Hydrogen Transfer Reactions with Quinones

The Effect of Pressure on Hydrogen Transfer Reactions with Quinones

High-Pressure Promoted Cycloadditions of Enol Ethers and 3-Aryl-2-cyano-2-propenoates

The Effect of Pressure on Organic Reactions

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