7‐Arylbicyclo[4.2.0]oct‐1‐ene – Synthese durch [2 + 2]‐Cycloadditionen von 1,2‐Cyclohexadien sowie 1‐Methyl‐1,2‐cyclohexadien und thermische Äquilibrierung der <i>exo/endo</i>‐Isomeren

Christl, Manfred; Schreck, Michael

doi:10.1002/cber.19871200609

Cited by 30 publications

(26 citation statements)

References 23 publications

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“…Based on previous studies, [7] we had anticipated a diradical intermediate with the achiral conformation 17 (Scheme 5) for the addition of (M)-or (P)-7 onto styrene and hence the complete loss of the stereochemical information introduced by 5. However, the mechanism of the styrene addition onto six-membered cyclic allenes had already proven to be interesting earlier, since on use of (Z)-b-deuteriostyrene the stereochemical information is entirely lost in the trapping of 1,2-cyclohexadiene, [3,7,8] but partially retained in the case of 1-oxa-2,3-cyclohexadiene [3] and completely retained with a 1-thia-5-aza-2,3-cyclohexadiene derivative. [3,9] Based on their result, Elliott et al [9] suggested the cycloaddition to be concerted and supported their view by quantum chemical calculations of a model system.…”

Section: Introductionmentioning

confidence: 99%

1‐Phenyl‐1,2‐cyclohexadiene: Astoundingly High Enantioselectivities on Generation in a Doering–Moore–Skattebøl Reaction and Interception by Activated Olefins

Christl

Fischer

Arnone

et al. 2009

Chemistry A European J

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The resolution of (1alpha,5alpha,6alpha)-6-bromo-6-fluoro-1-phenylbicyclo[3.1.0]hexane (rac-5) provided the enantiomerically pure precursors (-)-5 and (+)-5 of 1-phenyl-1,2-cyclohexadiene. On treatment of (-)-5 with methyllithium in the presence of 2,5-dimethylfuran, the pure (-)-enantiomer of the [4+2] cycloadduct of 2,5-dimethylfuran onto 1-phenyl-1,2-cyclohexadiene was obtained exclusively. From this result, it is concluded that pure (M)-1-phenyl-1,2-cyclohexadiene ((M)-7) emerged from (-)-5 and was enantiospecifically intercepted to give the product. In the case of indene as trap for (M)-7, the (-)- and the (+)-enantiomer of the [2+2] cycloadduct were formed in the ratio of 95:5. Highly surprising, remarkable enantioselectivities were also observed, when (M)-7 was trapped with styrene to furnish two diastereomeric [2+2] cycloadducts. Hence, the achiral conformation of the diradical conceivable as intermediate cannot play a decisive part. The enantioselective generation of (M)- and (P)-7 by the beta-elimination route was tested as well. Accordingly, 1-bromo-2-phenylcyclohexene was exposed to the potassium salt of (-)-menthol in the presence of 2,5-dimethylfuran, and the enantiomeric [4+2] cycloadducts of the latter onto (M)- and (P)-7 were produced in the ratio of 55:45.

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Section: Introductionmentioning

confidence: 99%

1‐Phenyl‐1,2‐cyclohexadiene: Astoundingly High Enantioselectivities on Generation in a Doering–Moore–Skattebøl Reaction and Interception by Activated Olefins

Christl

Fischer

Arnone

et al. 2009

Chemistry A European J

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“…The comparison of the temperature necessary for the above isomerisation with that required in the case of the styrene adducts of 1,2-cyclohexadiene, the equilibrium ratio endo/exo of which amounts to 1:13, [8] proves that the phenyl group at the six-membered ring of 10 does not accelerate the interconversion of the diastereomers.…”

Section: Introductionmentioning

confidence: 91%

“…In some cases, only the exo isomer was observed; in others, the endo compound emerged as the minor component of the isomeric mixture, [1] and 1 and two of its derivatives [1,3] as well as 1-oxa-2,3-cyclohexadiene [1, 10a] furnished both diastereomers in the same amount. The latter outcome is an unambiguous indication of the kinetic control of the product formation, since in the examples examined so far, namely, the styrene adducts of 1,2-cyclohexadiene, its 1-methyl derivative [8] and 1-oxa-2,3-cyclohexadiene, [10a] the exo diastereomer is the thermodynamically more stable one, as demonstrated by establishing the equilibrium by thermolysis. Accordingly, we now heated a solution of pure endo-10 in C 6 D 6 at 150-160 8C and noticed the generation of exo-10.…”

Section: Introductionmentioning

confidence: 96%

“…In addition, our 13 C NMR spectroscopic data are severely at variance with the published ones. [5] On the basis of the readily occurring rearrangement of the unsubstituted 6,6-dibromobicycloA C H T U N G T R E N N U N G [3.1.0]hexane [7] and its 1-methyl derivative, [8] it could not be expected that 5 is highly persistent at room temperature. In fact, it can be stored over extended periods only at À30 8C.…”

Section: Introductionmentioning

confidence: 99%

“…The ultimate goal of our studies was the enantioselective generation of 2, which permitted the examination of the stereochemical course of the cycloadditions onto 2. [6] Results and Discussion Preparation of the precursors for 2: The straightforward precursors for the title allene 2 are the dibromcarbene adduct 5 of 1-phenylcyclopentene and 1-bromo-2-phenylcyclohexene (8), which should release 2 by an a and a b elimination, respectively. Thus, we treated bromoform with KOtBu in the presence of 1-phenylcyclopentene and obtained the dibromophenylbicyclohexene 5 in 54 % yield (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

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1‐Phenyl‐1,2‐cyclohexadiene: Generation, Interception by Activated Olefins, Dimerisation and Trimerisation

Christl

Schreck

Fischer

et al. 2009

Chemistry A European J

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Four possible precursors of 1-phenyl-1,2-cyclohexadiene (2) were examined, namely, 6,6-dibromo-1-phenylbicyclo[3.1.0]hexane, (1alpha,5alpha,6alpha)-6-bromo-6-fluoro-1-phenylbicyclo[3.1.0]hexane, 1-bromo-2-phenylcyclohexene and 1-bromo-6-phenylcyclohexene. All four compounds could be converted into 2, as demonstrated by the products of the interception of 2 with activated olefins. Styrene, 1,1-diphenylethene, indene, furan and 2,5-dimethylfuran were employed as such. Whereas the first three gave [2+2] cycloadducts of 2, the last two provided one [4+2] cycloadduct each. To create the [2+2] cycloadducts, the pi bond of 2 that is more remote from the phenyl group reacted, whereas the pi bond of 2 conjugated with the phenyl group exclusively produced the [4+2] cycloadducts. The generation of 2 in the absence of a trapping reagent brought about relatively good yields of a dimer or a trimer of 2 depending on the mode of the liberation of 2. Being derivatives of triphenylene, the dimer as well as the trimer have unusual structures, thereby indicating that a phenyl group is participating in the formation of these compounds. The most surprising structure of the trimer was elucidated by X-ray crystal diffraction. As to the mechanisms, diradical intermediates are proposed both for the cycloadditions and for the dimerisation. The initial steps of the latter seem to proceed also in the trimerisation.

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3δ2-Chromene (2,3-Didehydro-2H-1-benzopyran): Generation and Interception

Christl¹,

Drinkuth

1998

Eur. J. Org. Chem.

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The treatment of 3‐bromo‐2H‐chromene (7), dissolved in furan, 2‐methylfuran, or 2,5‐dimethylfuran, with potassium tert‐butoxide, leads to formation of the epoxybenzo[c]chromene derivatives 8−11 in yields of 28−59%. Likewise, in styrene solution, exo‐2‐phenylcyclobuta[b]chromene 12 is produced (41% yield). With tetrahydrofuran as the solvent, 2‐tert‐butoxy‐2H‐chromene (13) is observed as the only product (79% yield). From these results, it is concluded that 7 is converted by β‐elimination into the title compound 5. This reactive intermediate is then intercepted by the furans and styrene in cycloaddition reactions to give compounds 8−12, whereas reaction with KOtBu/HOtBu transforms it to the acetal 13. The epoxybenzochromenes 8, 9, and 11 rearrange on heating at 110°C to give the epoxyxanthene derivatives 16−18.

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7‐Arylbicyclo[4.2.0]oct‐1‐ene – Synthese durch [2 + 2]‐Cycloadditionen von 1,2‐Cyclohexadien sowie 1‐Methyl‐1,2‐cyclohexadien und thermische Äquilibrierung der exo/endo‐Isomeren

Cited by 30 publications

References 23 publications

1‐Phenyl‐1,2‐cyclohexadiene: Astoundingly High Enantioselectivities on Generation in a Doering–Moore–Skattebøl Reaction and Interception by Activated Olefins

1‐Phenyl‐1,2‐cyclohexadiene: Astoundingly High Enantioselectivities on Generation in a Doering–Moore–Skattebøl Reaction and Interception by Activated Olefins

1‐Phenyl‐1,2‐cyclohexadiene: Generation, Interception by Activated Olefins, Dimerisation and Trimerisation

3δ2-Chromene (2,3-Didehydro-2H-1-benzopyran): Generation and Interception

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