Methylenecyclopropane Rearrangement as a Probe for Free Radical Substituent Effects. sigma (*) Values for Potent Radical-Stabilizing Nitrogen-Containing Substituents.

摘要: A series of nitrogen-containing 2-aryl-3,3-dimethylmethylenecyclopropanes have been prepared and rearrangement rates to the corresponding 2-arylisopropylidenecyclopropanes measured. These are dependent on nature group in para-position aryl group. Rearrangement used calculate σ • values, which a measure radical stabilizing ability substituent. Groups such as p-NN−Bu-t, p-CHN−Bu-t, p-NH2, p-CHN−OH, p-CHN−OCH3, “good” stabilizers. We also classified groups p-CHN−NMe2, p-NN−Ph, p-NN(O)-Bu-t, p-CHN(O)-Bu-t, p-CHN−O- M+, an extraordinarily large effect, “Super Stabilizers”. substituents stabilize transition state methylenecyclopropane by extensive spin delocalization. In case latter three substituents, nitroxyl type stabilization is proposed. Density functional calculations (B3LYP/6-31G*) carried out ...