Mechanistic Aspects of the Rearrangement and Elimination Reactions of α-Metalated Benzyl Alkyl Ethers

Lansbury, Peter T.; Pattison, Victor A.; Sidler, Jack D.; Bieber, Jerome B.

doi:10.1021/ja00953a016

Cited by 96 publications

(27 citation statements)

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“…Nach neueren Untersuchungen'2,20) uber diese Umlagerung und die analogen Ylid-Isomerisierungen verlaufen die Benzylwanderungen uber enge Radikalpaare nach folgendem Schema:…”

Section: Anmerkungen Zum Mechanismus Der Wittig-umlagerungunclassified

Heterocyclische 8π‐Systeme, 15. Untersuchungen über Indol‐2,3‐oxide: Herstellung von 3‐Hydroxyindolinen durch intramolekulare Wittig‐Umlagerung von 1,2‐Dihydro‐4H‐3,1‐benzoxazinen

Schmidt

Beitzke

1983

Chem. Ber.

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Beim Versuch, durch basenkatalysierte Ringverengung der 4H‐3,1‐Benzoxazine 3 die entsprechenden Indol‐2,3‐oxide 11 abzufangen, wurden im System KNH2/NH3 fl. die 3‐Hydroxy‐3H‐indole 7 isoliert. Die aus 3 mit FSO3CH3 hergestellten N‐Methylbenzoxazinium‐Salze 15 lieferten mit Ethoxid unter kinetischer Kontrolle die cis‐konfigurierten 1,2‐Dihydro‐4H‐3,1‐benzoxazine 19 diastereospezifisch. Die Thermolyse dieser Verbindungen über Chinonimine 26 wurde untersucht. Die Einwirkung von starken Basen auf 19 führte nicht zur 1,3‐Eliminierung, sondern zu einer supra‐suprafacialen Wittig‐Umlagerung unter Bildung der trans‐konfigurierten 3‐Hydroxyindoline 27. Für den Verlauf dieser in zweifachem Sinne intramolekularen Wittig‐Umlagerung wird ein intermediäres enges Radikalpaar vorgeschlagen.

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“…Nach neueren Untersuchungen'2,20) uber diese Umlagerung und die analogen Ylid-Isomerisierungen verlaufen die Benzylwanderungen uber enge Radikalpaare nach folgendem Schema:…”

Section: Anmerkungen Zum Mechanismus Der Wittig-umlagerungunclassified

Heterocyclische 8π‐Systeme, 15. Untersuchungen über Indol‐2,3‐oxide: Herstellung von 3‐Hydroxyindolinen durch intramolekulare Wittig‐Umlagerung von 1,2‐Dihydro‐4H‐3,1‐benzoxazinen

Schmidt

Beitzke

1983

Chem. Ber.

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“…The Wittig rearrangement of metallated benzyl ethers to benzyl carbinol salts proceeds with partial retention of configuration when optically active substrates are used (37) as does the Meisenheimer rearrangement (38). It now appears that stereoselective free radical cleavage -recombination processes are involved in both the Wittig (39,40) and Meisenheimer (38, 41) rearrangements. The chromic acid oxidation of tertiary hydrocarbons to tertiary alcohols proceeds with a high degree of retention of configuration and it has been suggested that this reaction also proceeds by a free radical pathway involving stereoselective cage recombination (42).…”

Section: Stereochemistry Of Cage Recombinationmentioning

confidence: 99%

Thermal decomposition of optically active unsymmetrical azoalkanes. (−)-(S)-1,1′-Diphenyl-1-methylazomethane

Kopecky¹,

Gillan²

1969

Can. J. Chem.

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The ratio, (k,/k,),,,., of the rate of coupling of the 1-phenylethyl radical with the benzyl radical to the rate of its rotation with respect to the benzyl radical in the solvent cage has been determined for several solvents. The optically pure title compound, (-)-(9-4, has been prepared and its absolute configuration determined. Thermal decomposition of (-)-(9-4 yields (-)-(R)-1,2-diphenylpropane, (-)-(R)-9, with partial retention of configuration. The maximum rotation of (-)-(R)-9 has been determined. At 100" in benzene, cyclohexane, chlorobenzene, (all containing ca. 1 M butanethiol) and butanethiol, the cage effects for the decomposition of (+)-4 were found to be 28.3, 31.7, 33.4, and 18.2%, respectively. Under these conditions (-)-(R)-9 was formed from (-)-(S)-4 with 10.3, 10.9, 13.0, and 17.3 % net retention of configuration, respectively. A simple expression for (k,/k,),,,, can be derived:(kclk3~~,e = F(1 -f )[(-)-(R)-9/(+ 1 4 9 -9 -1 I F i s the fraction of radicals consumed within the solvent cage and f is the fraction of radicals consumed within the solvent cage that disproportionate. Under the aboveconditions values for (k,/k,),,,, were found to be 0.059, 0.069, 0.090, and 0.070, respectively. The values of the cage effect and (k,/k,),,,, given were calculated assuming f = 0.1, but change little iff is assumed to be 0. The relevance of these results to the stereochemistry of the Wittig and Meisenheimer rearrangements and of the decomposition of diacyl peroxides is discussed.

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“…1 It has been proposed that the 1,2-Wittig rearrangement, could, in principle, involve either of the intermediates shown in Scheme 1 (R and R 1 are generally aryl and alkyl respectively), 1,2 and to support such mechanistic proposals, it has been shown that aldehydes are often byproducts of the reaction. 2 The migratory aptitudes of RЈ are in the order of free radical thermodynamic stabilities, 3 thus the radical pair mechanism for the reaction is favoured. 4 However the evidence in favour of a radical reaction is not overwhelming in all cases.…”

Section: Introductionmentioning

confidence: 99%

The gas phase 1,2-Wittig rearrangement is an anion reaction. A joint experimental and theoretical study

Sheldon¹,

Taylor²,

Bowie³

et al. 1999

J. Chem. Soc., Perkin Trans. 2

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Mechanistic Aspects of the Rearrangement and Elimination Reactions of α-Metalated Benzyl Alkyl Ethers

Cited by 96 publications

References 0 publications

Heterocyclische 8π‐Systeme, 15. Untersuchungen über Indol‐2,3‐oxide: Herstellung von 3‐Hydroxyindolinen durch intramolekulare Wittig‐Umlagerung von 1,2‐Dihydro‐4H‐3,1‐benzoxazinen

Heterocyclische 8π‐Systeme, 15. Untersuchungen über Indol‐2,3‐oxide: Herstellung von 3‐Hydroxyindolinen durch intramolekulare Wittig‐Umlagerung von 1,2‐Dihydro‐4H‐3,1‐benzoxazinen

Thermal decomposition of optically active unsymmetrical azoalkanes. (−)-(S)-1,1′-Diphenyl-1-methylazomethane

The gas phase 1,2-Wittig rearrangement is an anion reaction. A joint experimental and theoretical study

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