Istope effects in aromatization of 1,4-dihydrobenzene and 1,4-dihydronaphthalene with quinones

Müller, Paul; Joly, Daniel

doi:10.1016/s0040-4039(00)77399-0

Cited by 9 publications

(3 citation statements)

References 13 publications

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“…The value for 3d is the equilibrium constant for the two diastereomers which differ in configuration at the S-N chiral axis. The values for compounds 4 correspond to the ratio of regioisomers. Preliminary experiments suggest that this is an equilibrium ratio.…”

Section: Resultsmentioning

confidence: 99%

Stereochemistry in trivalent nitrogen compounds. 42. N-(Arylthio)benzimidazoles. Torsional barriers and 1,3 rearrangement

Raban¹,

Chang²,

Craine³

et al. 1985

J. Org. Chem.

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Section: Resultsmentioning

confidence: 99%

Stereochemistry in trivalent nitrogen compounds. 42. N-(Arylthio)benzimidazoles. Torsional barriers and 1,3 rearrangement

Raban¹,

Chang²,

Craine³

et al. 1985

J. Org. Chem.

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“…The high kinetic isotope effect of ca. 10 for perdeuterated 1,4-cyclohexadiene [8] and 1,4-dihydronaphthalene [26] could be taken as an indication for k;:,…”

Section: Synthesis Of Cis-and Tvuns-(36-d)-14-~yclohexadiene (La) mentioning

confidence: 99%

“…The high kinetic isotope effect of ca. 10 for perdeuterated 1,4cyclohexadiene [8] and 1,4-dihydronaphthalene [26] could be taken as an indication for ") [4] ' ) Extrapolated from chloranil, 100" [24]. ') [lo] a quasi-simultaneous breakage of two C-H bonds, but the argument is unconvincing in the light of isotope effects of 10 for hydride transfer from triphenylmethane dyes to quinones [27].…”

Section: Synthesis Of Cis-and Tvuns-(36-d)-14-~yclohexadiene (La) mentioning

confidence: 99%

Stereochemistry of Dehydrogenation of 1,4,‐Cyclohexadiene with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone

Müller

Joly

Mermoud

1984

Helvetica Chimica Acta

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Summarycis-and trans-(3,6-D2)-1 ,Ccyclohexadienes l a and l b have been synthesized from cis-3,4-dichlorocyclobutene (5). Aromatization to benzene with DDQ is cis-stereospecific with an uncertainty of 5 % . This result is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4-dihydroaromatics with 2,3-dichloro-5,6-dicyano-p -benzoquinone (DDQ).Introduction. -Oxidation of hydrocarbons with quinones proceeds via hydride transfer from the substrate to the quinone (mechanism A , Scheme 1) [l]. In agreement with this description, reaction rates of substituted toluenes with 2,3-dichIoro-5,6-dicyano-p-benzoquinone (DDQ) correlate with o giving a p-value of -4.3 [2]. Accordingly, substrates capable of forming stable carbenium ions upon hydride transfer exhibit enhanced reactivity. For example, cycloheptatriene reacts 200 times faster than 1,3-cycloheptadiene, and 1,2,3-triphenylcyclopropene ca. lo5 times faster than triphenylmethane [3] [4]. Similarly, vicinal dehydrogenation is believed to proceed in a stepwise manner (mechanism B ) involving sequential hydride and proton loss [5]. The partial cis-stereospecificity observed for dehydrogenation of acenaphthene has been ascribed to formation of an ion pair as reactive intermediate [6]. In contrast, dehydrogenation of 1 ,Ccyclohexadiene (1) and its benzannulated homologues does not fit this mechanistic picture. The reactivity of these compounds is usually about 100 times higher than that of 1,2-dihydroaromatics or similar model compounds, and it approaches that of cycloheptatrienes, provided that loss of two H-atoms from the allylic positions is possible [3-51. The enhanced rate of 1,6dihydroaromatics can be understood if it is assumed that part of the aromatic stabilization of the product is already reflected in the transition state of the reaction. This mechanistic hypothesis requires concerted loss of two H-atoms from the I,Cpositions, either in a cyclic mechanism (C) involving two cis-H-atoms, or in a cis-or trans-conjugate 1,Celimination (D). The cyclic mechanism C was proposed by Stoos & R o h k , when they found that cis-3,6-dimethyl-1 ,Ccyclohexadiene (2) reacts ca. 20 times faster than the trans-isomer 3 and 700 times faster than the 3,3-dimethyl derivative 4 [4]. Although the preference for cis-

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Cobalt‐Catalyzed Formal [4+2] Cycloaddition of α,α′‐Dichloro‐ortho‐Xylenes with Alkynes

2014

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A formal [4+2] cycloaddition of α,α′‐dichloro‐ortho‐xylenes with various alkynes has been developed using a low‐valent cobalt catalyst. The transformation has a wide substrate scope and high functional‐group tolerance and led to 1,4‐dihydronaphthalenes. The formed cycloadducts were easily aromatized with MnO2 under air. A mechanistic investigation suggests that the transformation proceeds through a benzyl cobaltation of alkyne, not the classical Diels–Alder reaction of ortho‐quinodimethanes. This methodology provides a straightforward and streamlined access to linearly expanded π‐conjugated aromatics.

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Istope effects in aromatization of 1,4-dihydrobenzene and 1,4-dihydronaphthalene with quinones

Cited by 9 publications

References 13 publications

Stereochemistry in trivalent nitrogen compounds. 42. N-(Arylthio)benzimidazoles. Torsional barriers and 1,3 rearrangement

Stereochemistry in trivalent nitrogen compounds. 42. N-(Arylthio)benzimidazoles. Torsional barriers and 1,3 rearrangement

Stereochemistry of Dehydrogenation of 1,4,‐Cyclohexadiene with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone

Cobalt‐Catalyzed Formal [4+2] Cycloaddition of α,α′‐Dichloro‐ortho‐Xylenes with Alkynes

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