Regiochemistry in radical cyclisations (4-exo-trig versus 5-endo-trig) of 2-halo-N-(3,4-dihydro-2-naphthyl)acetamides
作者:Masazumi Ikeda、Shinji Ohtani、Taeka Yamamoto、Tatsunori Sato、Hiroyuki Ishibashi
DOI:10.1039/a801714j
日期:——
The regioselectivity in Bu3SnH-mediated radical cyclisations (4-exo-trig versus 5-endo-trig) of a range of 2-halo-N-(3,4-dihydro-2-naphthyl)acetamides has been examined from the standpoint of the effects of substituents on the radical centre and on the nitrogen atom as well as the reaction temperature. When the substituent on the radical centre is a hydrogen or chlorine atom, 4-exo-trig cyclisation (β-lactam formation) is favoured in boiling toluene, while radical stabilising substituents such as methyl, phenyl, phenylthio, dimethyl and dichloro groups bring about 5-endo-trig cyclisation (γ-lactam formation) predominantly or exclusively. In boiling benzene, however, the predominant formation of β-lactam is observed for the methyl-substituent. On the other hand, no remarkable difference in the product distributions between the methyl and benzyl substituents on the nitrogen atom is observed. These results are discussed in terms of kinetic or thermodynamic considerations.
从自由基中心和氮原子上的取代基以及反应温度的影响角度,研究了一系列 2-卤代-N-(3,4-二氢-2-萘基)乙酰胺在 Bu3SnH 介导的自由基环化(4-外向-三反应与 5-内向-三反应)中的区域选择性。当自由基中心上的取代基为氢原子或氯原子时,在沸腾的甲苯中有利于 4-外三旋环化(β-内酰胺的形成),而甲基、苯基、苯硫基、二甲基和二氯基团等自由基稳定取代基则主要或完全导致 5-内三旋环化(γ-内酰胺的形成)。但在沸腾的苯中,甲基取代基主要形成 β-内酰胺。另一方面,氮原子上的甲基和苄基取代基在产物分布上没有明显差异。我们从动力学或热力学的角度对这些结果进行了讨论。