Stereochemistry.  XLIII.  Racemizations and solvolyses of cyclopropanes through carbanion-carbonium ion intermediates

Yankee, Ernest W.; Badea, F.; Howe, Norman E.; Cram, Donald J.

doi:10.1021/ja00794a016

Cited by 41 publications

(9 citation statements)

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“…Cram and co-workers observed that the optically active cyclopropane derivative 40 racemizes with a half-life of 133 min in MeOH at 1258 [53]. The further reaction at 1508 corresponds to a carbocationic S n 1-type behavior, indicating an equilibrium with the zwitterion 39 (Scheme 12).…”

Section: Methodsmentioning

confidence: 99%

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Mulzer

Huisgen

Arion

et al. 2011

Helvetica Chimica Acta

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Dedicated to Paul von Ragué Schleyer, friend and mentor, on the occasion of his 80th birthday Kinetic measurements for the thermal rearrangement of 2,2-diphenyl-1-[(E)-styryl]cyclopropane (22a) to 3,4,4-triphenylcyclopent-1-ene (23a) in decalin furnished DH = isom ¼ 31.0 AE 1.2 kcal mol À1 and DS = isom ¼ À 6.0 AE 2.6 e.u. The lowering of DH = by 20 kcal mol À1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (þ)-(S)-22a proceeds with DH = rac ¼ 28.2 AE 0.8 kcal mol À1and DS = rac ¼ À 5 AE 2 e.u., and is at 1508 106 times faster than the rearrangement. Seven further 1-(2-arylethenyl)-2,2-diphenylcyclopropanes 22, (E)-and (Z)-isomers, were synthesized and characterized. The (E)-compounds showed only modest substituent influence in their k rac (at 119.48) and k isom (at 159.38) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log k rac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring-opening of the preponderant s-trans-conformation of 22 gives rise to the 1-exophenylallyl radical 26 that bears the diphenylethyl radical in 3-exo-position, and is responsible for racemization. The 1-exo-3-endo-substituted allylic diradical 27 arises from the minor s-gaucheconformation of 22 and is capable of closing the three-or the five-membered ring, 22 or 23, respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum-chemical calculations by Houk et al. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate?

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Section: Methodsmentioning

confidence: 99%

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Mulzer

Huisgen

Arion

et al. 2011

Helvetica Chimica Acta

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“…As another small strained ring, cyclopropanes were found to form either polar P3 biradicals or zwitterions, depending on subtle changes in substituents, according to Cram and coworkers 132–135. Applying these compounds as initiators, ethyl 1‐cyano‐2‐( p ‐methoxyphenyl)cyclopropanecarboxylate when heated with acrylonitrile gave free radical homopolymer,136 but with NVCz gave cationic homopolymer 137.…”

Section: Introductionmentioning

confidence: 99%

A paradigm for the mechanisms and products of spontaneous polymerizations

Hall

Padías

2009

J. Polym. Sci. A Polym. Chem.

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“…[9H]fluorene) (13), [43] dibenzofulvene (14), [44] trans-1,2-diphenylcyclopropane (15), [45] trans-2,3-dicyanospiro(cyclopropane-1,9'-[9H]fluorene) (18), [46] 2-cyanospiro(cyclopropane-1,9'-[9H]fluorene) (19) [46] and 2,2-diphenylcyclopropanecarbonitrile (21) [47] have been identified by comparison of the NMR spectra with literature data. were carefully deoxygenated by three freeze-thaw cycles.…”

Section: Methodsmentioning

confidence: 99%

Reactions of Diazo Compounds with Alkenes Catalysed by [RuCl(cod)(Cp)]: Effect of the Substituents in the Formation of Cyclopropanation or Metathesis Products

Basato

Tubaro

Biffis

et al. 2009

Chemistry A European J

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The reaction of diazo compounds with alkenes catalysed by complex [RuCl(cod)(Cp)] (cod = 1,5-cyclooctadiene, Cp = cyclopentadienyl) has been studied. The catalytic cycle involves in the first step the decomposition of the diazo derivative to afford the reactive [RuCl(Cp){=C(R(1))R(2)}] intermediate and a mechanism is proposed for this step based on a kinetic study of the simple coupling reaction of ethyl diazoacetate. The evolution of the Ru-carbene intermediate in the presence of alkenes depends on the nature of the substituents at both the diazo N(2)=C(R(1))R(2) (R(1), R(2) = Ph, H; Ph, CO(2)Me; Ph, Ph; C(R(1))R(2) = fluorene) and the olefin substrates R(3)(H)C=C(H)R(4) (R(3), R(4) = CO(2)Et, CO(2)Et; Ph, Ph; Ph, Me; Ph, H; Me, Br; Me, CN; Ph, CN; H, CN; CN, CN). A remarkable reactivity of the complex was recorded, especially towards unstable aryldiazo compounds and electron-poor olefins. The results obtained indicate that either cyclopropanation or metathesis products can be formed: the first products are favoured by the presence of a cyano substituent at the double bond and the second ones by a phenyl.

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Stereochemistry. XLIII. Racemizations and solvolyses of cyclopropanes through carbanion-carbonium ion intermediates

Cited by 41 publications

References 0 publications

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

A paradigm for the mechanisms and products of spontaneous polymerizations

Reactions of Diazo Compounds with Alkenes Catalysed by [RuCl(cod)(Cp)]: Effect of the Substituents in the Formation of Cyclopropanation or Metathesis Products

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