Stereoelectronic and Resonance Effects on the Rate of Ring Opening of <i>N</i>-Cyclopropyl-Based Single Electron Transfer Probes
作者:Michelle L. Grimm、N. Kamrudin Suleman、Amber N. Hancock、Jared N. Spencer、Travis Dudding、Rozhin Rowshanpour、Neal Castagnoli、James M. Tanko
DOI:10.1021/jacs.9b12617
日期:2020.2.5
poor probe for single electron transfer (SET) because the corresponding radical cation undergoes cyclopropane ring opening with a rate constant of only 4.1 x 104 s-1, too slow to compete with other processes such as radical cation deprotonation. The sluggish rate of ring opening can be attributed to either (i) a resonance effect in which the spin and charge of the radical cation in the ring-closed form
N-环丙基-N-甲基苯胺 (5) 是单电子转移 (SET) 的不良探针,因为相应的自由基阳离子以仅 4.1 x 104 s-1 的速率常数进行环丙烷开环,速度太慢而无法与其他过程竞争如自由基阳离子去质子化。开环速度缓慢可归因于 (i) 共振效应,其中闭环形式的自由基阳离子的自旋和电荷离域到苯环中,和/或 (ii) 最低能量构象SET 产物 (5•+) 不满足环丙烷开环的立体电子要求。为了解决这个问题,设计了一系列新的 N-环丙基苯胺来将环丙基锁定为所需的开环所需的二等分构象。结果表明,衍生自 1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline] (6) 和 6'-的自由基阳离子的开环速率常数chloro-1'-methyl-3',4'-dihydro-1'H-spiro[cyclopropane-1,2'-quinoline]