Specific photochemical behavior of pyrazolines and construction of its electron transfer system

近年来，人们对环状偶氮烷烃通过光诱导电子转移（PET）反应生成的自由基阳离子进行了研究，并通过重排和溶剂加成反应生成了一些特征化合物。当生成的自由基阳离子由于其几何约束和稳定性而具有重排的可能性时，反应机制变得复杂，因为这些物种似乎参与脱氮。在我们以前的研究中，使用1-吡唑啉和9，10-二氰基蒽（DCA）作为电子接受敏化剂，PET反应被发现引起涉及自由基阳离子中间体的芳基迁移。尽管事实上保留氮的自由基阳离子的行为是相当令人感兴趣的，但是通过PET反应没有获得保留氮的产物，并且产物是消除氮的化合物。在这个项目中，我们报告的第一个例子中使用的环状偶氮烷烃的PET反应，其中氮保留的产品是从自由基阳离子物种的3-亚烷基-1-吡唑啉具有环外双键，并成功地检测到的氮保留的自由基阳离子是通过激光闪光光解（LFP）技术完成的。

Radical cations generated from cyclic azoalkanes by photoinduced electron transfer (PET) have recently been investigated and produced a few characteristic compounds by rearrangements and solvent additions. The reaction mechanisms become complex when the generated radical cations have the possibility of rearranging due to their geometric constraints and stabilities, as these species appear to be involved in denitrogenation. In our previous studies using the 1-pyrazolines and 9, 10-dicyanoanthracene (DCA) as an electron accepting sensitizer, the PET reaction was found to cause aryl migration involving the radical cation intermediates. In spite of the fact that the behavior of the nitrogen-retained radical cations are of considerable interest, nitrogen-retained products by the PET reaction have not been obtained, and the products are nitrogen-eliminated compounds. In this project, we report the first example of the use of cyclic azoalkanes for the PET reaction in which nitrogen-retained products are obtained from the radical cation species of 3-alkylidene-1-pyrazolines having an exocyclic double bond, and that the successful detection of the nitrogen-retained radical cations was accomplished by a laser flash photolysis (LFP) technique.