Mechanistic studies of direct and sensitized photolysis of methyl (4-nitrophenyl)diazoacetate in the presence of an electron-donating amine: photochemical generation of the diazoalkane radical anion
作者:Tadashi Mizushima、Go Monden、Shigeru Murata、Kunihiko Ishii、Hiro-o Hamaguchi
DOI:10.1039/b202800j
日期:2002.6.27
The direct and perylene-sensitized photolysis of methyl (4-nitrophenyl)diazoacetate (1) in the presence of an electron-donating amine was investigated by the characterization of reaction products and by the direct observation of reactive species using a laser flash photolysis technique. In the direct photolysis of 1 in the presence of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), electron transfer from TMPD occurs and the photoproducts are obtained through an intermediate other than the carbene 3, which we suppose to be the carbene radical anion 3−˙. In the perylene-sensitized photolysis of 1 in the presence of an amine having a large electron-donating ability such as N,N-dimethylaniline
and TMPD, the radical anion of 1 can be generated by perylene-mediated electron transfer from the amine to 1. The resulting 1−˙ appears to undergo extrusion of dinitrogen to give 3−˙ smoothly, the behavior of which is dependent on the amine employed as an additive. The product studies revealed that 3−˙ reacts readily with O2 to give the ketoester 5 or abstracts hydrogen atoms to give the ester 7, which is not inconsistent with the theoretical prediction that 3−˙ has a σ radical character in its electronic structure.
通过反应产物表征和激光闪光光解技术直接观察活性物种,研究了在电子供体胺存在下,甲基(4-硝基苯基)重氮乙酸酯(1)的直接和苊醌敏化光解反应。在直接光解1的过程中,当有N,N,N′,N′-四甲基-p-苯二胺(TMPD)存在时,发生从TMPD的电子转移,光产物是通过中间体产生的,而非卡宾3,我们推测该中间体为卡宾自由基阴离子3−˙。在苊醌敏化下,当存在强电子供体胺如N,N-二甲基苯胺和TMPD时,可通过苊醌介导的从胺到1的电子转移生成1的自由基阴离子。所生成的1−˙看似能顺利排出二氮生成3−˙,其行为取决于所添加的胺。产物研究表明,3−˙易于与氧气反应生成酮酯5或抽取氢原子生成酯7,这与理论预测3−˙在其电子结构中具有σ自由基特性是一致的。