1,2‐Carbonylverschiebung unter Dehydrierung in 1,5‐Dimethylbicyclo[3.3.0]octan‐3,7‐dion

Quast, Helmut; Herkert, Thomas; Klaubert, C. A.

doi:10.1002/jlac.198719870856

Cited by 18 publications

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References 58 publications

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“…Modified from a procedure described for the 1,5-dimethyl compounds. 36 Sodium borohydride (40 g, 1.1 mol) was added in portions to a stirred, cooled (0-20 °C) solution of 6 (36.0 g, 0.2 mol) in methanol (0.8 L). Stirring was continued for 3 d. Water (0.4 L) was added, and the solution was acidified with concentrated hydrochloric acid (120 mL) to attain a pH value of 5.…”

Section: Methodsmentioning

confidence: 99%

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Lifting of the Degeneracy in Semibullvalenes by Remote and Direct Substituents: A Quantitative Study Using Variable-Temperature Carbon-13 NMR Spectroscopy

Heubes¹,

Dietz²,

Quast³

et al. 2001

J. Org. Chem.

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A series of six 1,5-(ethylmethyl)semibullvalenes (1a <==> 1a', 2 <==> 2', 3 <==>3') and two 4(2)-substituted semibullvalenes (4 <==> 4'), each undergoing Cope equilibria between nondegenerate valence tautomers, was investigated by carbon-13 NMR spectroscopy at a range of temperatures in several different solvents. Gompper's treatment of substituent perturbation was extended, specifically accounting for the effects of the substituents on chemical shifts, to allow the determination of the thermodynamic parameters for these skewed equilibria. These new treatments were used to determine the population difference (f - f ') between the valence tautomers and the perturbation thermodynamic quantities DeltaH(P), DeltaS(P), and DeltaG(P). The slow-exchange limit was reached for the parent 1,5-(ethylmethyl)semibullvalenes 3a<==> 3a' from which it was established that the preferred valence tautomer is 3a with the ethyl group on the cyclopropane ring. Despite considerable effort, the slow-exchange limit could not be reached in any of our other remotely substituted semibullvalenes. Provided that the ethyl group always prefers the cyclopropyl position as in 3a, the 1-ethyl-5-methylsemibullvalenes 1a, 2, and 3 are more stable by DeltaH(P) = 0.7-1.7 kJ mol(-1) than their valence tautomers 1a', 2', and 3'. In the directly substituted semibullvalenes (4 left harpoon ovet right harpoon 4'), the preferred valence tautomers 4a and 4b have the bromine atom or the nitrile group on the vinyl position (C(4)) rather than on the cyclopropane ring (C(2)) and are more stable than 4a' and 4b' by DeltaH(P) = 4.8 and 7.0 kJ mol(-1), respectively.

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Section: Methodsmentioning

confidence: 99%

“…1-Ethyl-5-methylbicyclo[3.3.0]octane-3,7-dioles (7, M ixture of D iastereomers). Modified from a procedure described for the 1,5-dimethyl compounds . Sodium borohydride (40 g, 1.1 mol) was added in portions to a stirred, cooled (0−20 °C) solution of 6 (36.0 g, 0.2 mol) in methanol (0.8 L).…”

Section: Methodsmentioning

confidence: 99%

Lifting of the Degeneracy in Semibullvalenes by Remote and Direct Substituents: A Quantitative Study Using Variable-Temperature Carbon-13 NMR Spectroscopy

Heubes¹,

Dietz²,

Quast³

et al. 2001

J. Org. Chem.

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Stereochemie der Hydrocyanierung von 1,5‐Dimethylbicyclo[3.3.0]octanonen und ‐octenonen

et al. 1988

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3,7‐Dicyan‐2,6‐dimethoxy‐1,5‐dimethylsemibullvalen

1988

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Michael-Addition vonMethylmalonsiiuredimethylester an Acrylnitril f i r t mit 92% Ausbeute zum Diesternitril 4a, das quantitativ zur Monosiiure 4b hydrolysiert wird. D e m Kolbe-Elektrolyse ergibt mit 21% Ausbeute ein (1:l)-Gemisch der diastereomeren Bis(esternitri1e) meso-und rue-5. Bei der DieckmannKondensation dieses Gemischs mit Kalium-tert-butylat erhglt man aus meso-5 mit 54% Ausbeute das monocyclische u-Cyanketon 6% aus rac-5 mit 68% Ausbeute das bicyclische Bis(&cyan-enol) 7c. (relativ zu der des 3,7-Dicyansemibullvalens la) um 17 kJmol-' entspricht.Semibullvalene sind unter anderem interessant fur den Vergleich molekularer Eigenschaften in Losung und im festen Zustand. So zeigt das unsubstituierte Semibullvalen extrern schnelle entartete Cope-Umlagerung in Losung2). Auch in einer bestimmten festen Phase lagert sich Semibullvalen urn, doch ist die Cope-Umlagerung nicht mehr entartet. In einer zweiten festen Phase ist sie schlieBlich ,,eingefroren"').Fur die isomeren Dicyan-l,5-dimethylsemibullvalene 1 a4) und 2a5) gibt es keinen Zusammenhang zwischen der Geschwindigkeit ihrer Cope-Umlagerung in Losung und den durch Rontgenstrukturbestimmung ermittelten Atomabstanden C(2) -C(8) und C(4)..C(6). Zwei Bromatome an den Enden der Allylsysteme des 3,7-Dicyansemibullvalens 1 a verzogern stark die entartete Cope-Umlagerung. So lagert sich das 2,4-Dibromsemibullvalen 1 b 6000ma1, das 2,6-Dibromsemibullvalen l c 1300mal (bei 200 K) langsamer um als die nicht bromierte Verbindung 1 a. Die Atomabstande C(2)-C(8) und C(4)...C(6) in Einkristallen von 1 a und b sind verschieden, bei 1 c jedoch scheinbar gleich groB. Dieses existiert somit hochst wahrscheinlich in einem plastisch-kristallinen festen Zustand 6, mit statistischer Orientierungsfehlordnung beziiglich der pseudo-zweizahligen Achse senk- Michael reaction of dimethyl methylmalonate and acrylonitrile affords a 92% yield of the diesternitrile 4a, which is quantitatively hydrolysed to give the monoacid 4b. When subjected to Kolbe electrolysis, 4b produced a 1 : 1 mixture (21 % yield) of the diastereomeric bis(esternitri1es) mso-and rac-5. In the Dieckmann condensation of this mixture with potassium tert-butoxide, meso-5 furnishes 54% of the monocyclic a-cyanoketone 6a while ruc-5 affords 68% of the bicyclic bis(fkyanoeno1) 7c. The products of the condensation exist predomlnantly in these tautomeric forms (68 and 7% respectively) and are separated on the basis of their diflrerent acidity. Diazomethane methylates 7c to provide the bis(&cyanoenolether) 10 (79% yield), which is brominated by Nbromosuccinimide to yield the bis(bromo-P-cyanoenolether) 11 (51 % yield). Zinc/copper reagent debrominates 11 to afford the title compound Id (49% yield). The rate constants of the degene- Man kommt daher mit wenigen Schritten aus.

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1,2‐Carbonylverschiebung unter Dehydrierung in 1,5‐Dimethylbicyclo[3.3.0]octan‐3,7‐dion

Cited by 18 publications

References 58 publications

Lifting of the Degeneracy in Semibullvalenes by Remote and Direct Substituents: A Quantitative Study Using Variable-Temperature Carbon-13 NMR Spectroscopy

Lifting of the Degeneracy in Semibullvalenes by Remote and Direct Substituents: A Quantitative Study Using Variable-Temperature Carbon-13 NMR Spectroscopy

Stereochemie der Hydrocyanierung von 1,5‐Dimethylbicyclo[3.3.0]octanonen und ‐octenonen

3,7‐Dicyan‐2,6‐dimethoxy‐1,5‐dimethylsemibullvalen

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