72138-31-9Relevant academic research and scientific papers
Methylenecyclopropane Rearrangement as a Probe for Free Radical Substituent Effects. Effect of Sulfur in Variouis Oxidation States
Creary, Xavier,Mehrsheikh-Mohammadi, M. E.
, p. 1110 - 1114 (1986)
A series of 3-aryl-2,2-dimethylmethylenecyclopropanes 4 with the sulfur-containing substitutents SCH3, SOCH3, SO2CH3, and PS(OEt)2 in the para and meta positions have been prepared.These substrates undergo thermal rearrangement at 80 deg C in C6D6 to give the corresponding 2-arylisopropylidenecyclopropanes 5 at rates which vary as a function of substituent.The para-substituted substrates all rearrange at faster rates than the unsubstituted system.Comparison with the meta isomers suggests that the rate-enhancing effect is conjugative in nature.The singlettrimethylenemethane biradical intermediate is suggested to be stabilized by p-SCH3, p-SOCH3, and p-SO2CH3 substituents, with p-SCH3 providing the greatest stabilization.The p-PS(OEt)2 substituents is also quite effective at increasing rate.These rate effects are considered in terms of interaction of the nonbonding electron pair of SCH3 with the developing benzylic radical center.A further stabilizing interaction involving vacant d orbitals is considered to account for the greater stabilizing effect of SCH3 relative to OCH3, as well as the relatively large stabilizing effects of SOCH3, SO2CH3, and PS(OEt)2 on the transition state for this methylenecyclopropane rearrangement.
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.
