65354-71-4Relevant articles and documents
Cobalt- and Silver-Promoted Methylenecyclopropane Rearrangements
Creary, Xavier
, p. 136 - 144 (2018/02/19)
The rate of the methylenecyclopropane rearrangement is enhanced by an alkyne-Co2(CO)6 complex bonded to the para position of a benzene ring. This is explained by a stabilizing effect on the transition state leading to the biradical intermediate. Computational studies indicate that the benzylic-type biradical intermediate is stabilized by a delocalization mechanism, where spin is delocalized onto the two cobalt atoms. Silver cation also enhances the rate of the methylenecyclopropane rearrangement. Computational studies suggest that silver cation can also stabilize a benzylic radical by spin delocalization involving silver. In the case of the silver-promoted reactions, the rate enhancements in a series of aryl-substituted methylenecyclopropanes correlate with σ+ values. The question remains open as to whether the silver-catalyzed methylenecyclopropane rearrangement proceeds via an argento-stabilized biradical or whether the reaction involves an argento-substituted allylic cation.
Rearrangement of 2-Aryl-3,3-dimethylmethylenecyclopropanes. Substituent Effects on a Nonpolar Radical-Like Transition State
Creary, Xavier
, p. 280 - 284 (2007/10/02)
The effect of substituents on the thermal rearrangement of 2-aryl-3,3-dimethylmethylenecyclopropanes, 4, to 2-arylisopropylidenecyclopropanes, 5, has been determined.This has allowed an evaluation of substituent effects on a free-radical-like transition state devoid of polar character.In general, no correlation of all the data could be obtained with Hammett ? values.Electronegative meta substituents slightly decreased rates (ρ = -0.16).Conjugating substituents such as CN and CO2CH3 in the para position increased rates.The effect of the p-CF3 group was rate enhancing.The potential for C-F hyperconjugative stabilization is discussed as a radical-stabilizing feature.Thiomethyl and trimethylsilyl substituents in the para position increased rates.The possibility of radical-stabilizing interactions with vicinal ?* and ? orbitals is discussed. p-Methoxy substitution increased rates while p-fluoro substitution slowed rates.Resonance delocalization involving charge-separated forms 10a and 11 was suggested to be less favorable in the case of p-fluoro substitution.Delocalization involving an expanded octet accounted for increased rearrangement rates of p-Cl and p-Br-substituted 4.
