Zur Thermolyse des Bicyclo[2.1.0]pentan‐5‐spiro‐cyclopropans

Roth, Wolfgang R.; Enderer, Klaus

doi:10.1002/jlac.19707330106

Cited by 20 publications

(5 citation statements)

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“…A great deal of experimental work has been done on the stereochemistry of rearrangement of various substituted spiropentanes to the corresponding methylenecyclobutanes. − The upshot is that the reaction shows some stereoselectivity but not complete stereospecificity. This result has been interpreted as evidence for a competition between stepwise and concerted pericyclic mechanisms for the reaction .…”

Section: Resultsmentioning

confidence: 99%

Ab Initio Calculations on the Formation and Rearrangement of Spiropentane

2009

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The formation of spiropentane, by addition of singlet (1A1) methylene to methylenecyclopropane, and the unimolecular reactions of spiropentane have all been studied computationally. Benchmark calculations on two key biradicals were conducted by the multireference Mukherjee's coupled-cluster (MkCC) method. Various single-reference coupled-cluster methods and multireference second-order perturbation theory were then compared for accuracy against experimental data and the MkCC results. The object of the exercise was to get the best possible description of the potential energy surface for formation and reactions of spiropentane, as a prelude to molecular dynamics simulation of the reactions. The principal conclusions of the study were that none of the unimolecular reactions of spiropentane can be classified as pericyclic processes and that the observed stereoselectivities are probably of dynamical origin. A possible resolution of a disagreement between two studies on the dynamics of cyclopropanation reactions is also offered. Of the various approximate computational models evaluated in this study, the best fit came from a composite coupled-cluster approach in which the lower-energy result was selected from a restricted coupled-cluster and a broken-symmetry, unrestricted coupled-cluster calculation on each stationary point. However, such an approach is not strictly defensible, since coupled-cluster methods are not variational, and so further evaluation of its validity would be desirable.

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Section: Resultsmentioning

confidence: 99%

Ab Initio Calculations on the Formation and Rearrangement of Spiropentane

2009

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“…Fur eine in struktureller Hinsicht ahnliche Keaktion, namlich die thermische Isomerisierung der stereoisomercn 6,7-Diniethyl-bicyclo[3.2.0]hept-6-ene, wurde ein radiltalischer Verlauf gesichert [29]. Im Falle des Zwischenproduktes 32 wurde eine radikalisclie Umwandlung zu dem stabilen Benzylalkyl-diradika135 fuhren, das dann zu exo-und endo-17 abreagieren kann.…”

Section: C-3) Was Fur Beide Prozesse Einen Konzertierten Verlauf Wenunclassified

Photochemisches Verhalten von 1‐ und 2‐alkylierten 1,2‐Dihydronaphtalinen

Heimgartner

Ulrich

Hansen

et al. 1971

Helvetica Chimica Acta

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Irradiation of 1-alkyl-substituted 1,2-dihydronaphthalenes (10, 11, 12) with a lowpressure mercury lamp yields by ring opening w-vinyl-o-quinodimethanes, which undergo [l, 71 H-shifts to give 1,2-divinyl-benzenes (8, 18, 23; cf. schemes 2 , 3 and 4). In a further photoreaction of the divinylbenzenes, benzobicyclo[3.l.0]hex-2-enes (17,19,22) are formed. Z-f~lkyl-suhstit~ited 1,2-dihydronaphthalenes (13, 14, 15, 16) are transformed by irradiation into o-vinyl-o-quinoclimethanes, which show [l, 71 H-shifts to yield in this case 2-(buta-l', 3'-dienyl)-toluencs (9, 25, 26, 27; cf. schemes 6 and 7). The irradiation of 1-methyl-(10) and 1-ethyl-1,2-dihydronaphthalene (11) with a high-pressure mercury lamp produces, besides the products of irradiation using the lowpressure lamp, 2-ethyl-allenylbenzene (24), and (from 11) 4-exo-ethyl-benzobicyclo[3.1.0]hex-2ene (exo-20) and 2-propyl-allenylbenzenc (21), respectively (cf. scheme 5). Obviously, these products arise from a photoreaction of thc primarily formed w-vinyl-o-quinodimethanes a. 5 1 R -6 7 8 9 2. Herstellung der 1,2-Dihydronaphtaline. ~ k-ur die photocheniischen Versuclir wurden die in Formelschema 1 aufgefiihrten 1,Z-Dihydronaphtaline hergestellt. 10, 11, 13, 15 und 16 wurden nach Standardniethoden iiber eine Malonesterkondensation iiiit den entsprechenden I'l~envlalkvll~roiiiiden gemass dem fur die Synthese HELVETICA C H I M I C~ -\CTA 1-01 54, Fasc 7 (1971) ~ Nr. 256 231 5 von 11 wiedergegebenen Reaktionsschema gewonnen. Die analoge Herstellung von 15 und 16 ist in der Literatur beschrieben (vgl. [lo] bzw. [ll]). 4. PPS 5. LiAlH4 ~~~~~~ 9 -6. H3P04 COOH 1. CHZ (COOCZH5)2 11 PPS = Polyphosphorsaure Formelschema 1 10 11 12 C03 C03 ii6 -12 13 14 15 16Die Alkylierungen des Malonsaure-diathylesters waren in allen Fallen von Bromwasserstoffeliminierungen begleitet, so dass die Ausbeuten an alkylierten Malonsaure-diathylestern in der Regel 50% nicht uberstiegen. Die Herstellung von 15 gelang nur iiber die Methylierung des nach dem ersten Schritt erhaltenen /3-Phenylisopropylmalonsaure-diathylesters (vgl. [lo]). Versuche, Methylmalonsaure-diathylester direkt mit P-Phenylisopropylbromid zu alkylieren, fuhrten ausschliesslich zur Rroinwasserstoffabspaltung aus dem Bromid.Bei der Wasserabspaltung aus den entsprechenden 1-Tetralolen mit 85-proz. Phosphorsaure bei 110" traten stets auch die entsprechenden Naphtaline in Mengen his zu 10% auf 2). Die Naphtaline liessen sich leicht durch Chroniatographie der Reaktionsprodukte an Kieselgel, das niit 10% Pikrinsaure beladen war, mittels Elution mit Pentan entfernen. 2,Andere Wasserabspaltungsmethoden, z . B . Phosphoroxychlorirl/Pyridin, lieferten grosserc Mengen der Naphtaline. 13 und 15 wurden aus den entsprechenden LTetralolen durch Erhitzen mit 9-Toluolsulfonsaurechlorid/Pyridin im Eombenrohr auf 140" gewonnen. 231r1 HI~LVRTIC.\ ( ' H I M I C A ,\(:TA ~ \-ol. 54, 1;asc. 7 (1971) -. XI-. 250 1 0 -2~) rnit einer Niederdrucklampe bestrahlt. Es entstehen wieder die Photoprodukte exo-17 und endo-17, wobei exo-17 mengenmassig iiber...

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“…On thermolysis it gives products totally different from 18, which is the parent hydrocarbon of the spiro system present in 14.20•21 A homolytic pathway from 16 to 14 by way of a spiropentanecontaining isomer can be written, but this is also unlikely, as the parent spiropentane hydrocarbon 19 rearranges in the reverse direction at 150 °C to form 17. 21 In contrast to these objections, the acid-catalyzed shift in eq 318 is mechanistically unexceptional.…”

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confidence: 99%