Structural Effects on the β-Scission Reaction of Tertiary Arylcarbinyloxyl Radicals. The Role of α-Cyclopropyl and α-Cyclobutyl Groups
作者:Massimo Bietti、Giacomo Gente、Michela Salamone
DOI:10.1021/jo050883i
日期:2005.8.1
α-dicyclopropylphenylmethoxyl (2•) radicals undergo β-scission to give cyclopropyl phenyl ketone as the major or exclusive product with rate constants higher than that measured for the cumyloxyl radical. It is proposed that in the transition state for β-scission of 1• and 2•, formation of the CO double bond is assisted by overlap with the C−C bonding orbitals of the cyclopropane ring. With tertiary arylcarbinyloxyl
已经对带有α-环丙基和α-环丁基的叔芳基甲氧羰基自由基的反应性进行了产物和时间分辨的动力学研究。1-环丙基-1-苯基乙氧基(1 •)和α,α-二环丙基苯基甲氧基(2 •)自由基均经过β断裂,以环丙基苯基酮为主要或专有产物,其速率常数高于对枯基氧基的测定。 。有人提出在1 •和2 •的β分裂的过渡态中,C的形成O双键与环丙烷环的C-C键轨道重叠而得到辅助。对于带有α-环丁基的叔芳基甲氧羰基自由基,例如1-环丁基-1-苯基乙氧基(4 •)和1-环丁基-1-苯基丙氧基(5 •)自由基,区域选择性的选择主要取决于所形成自由基的稳定性。通过β分裂。因此,4 •进行了独家的C-环丁基键裂解而得到苯乙酮,而5 •则观察到C-环丁基和C-乙基键裂解之间的竞争,导致了丙苯酮和环丁基苯基酮的比例为2:1。