Enamine-derived radicals are crucial intermediates in singly occupied molecular orbital (SOMO) catalysis. However, observing them directly is elusive and remains a long-standing challenge. Here, an advanced time-resolved electron paramagnetic resonance technique was employed to characterize and monitor the key intermediates in photoredox transformations by primary aminocatalysis on a microsecond timescale. The transient enamine radical cation, generated by single electron transfer (SET), and the deprotonated form of α-imino radical intermediates were directly observed for the first time, both spectroscopically and kinetically. In reactions with styrene, enamine radical cation was found to be faster than α-imino radical by one order of magnitude. This revealed the subtle role of deprotonation associated with secondary enamine radical cation in the photoredox transformations by primary aminocatalysis.

烯胺衍生的自由基是单占据分子轨道（SOMO）催化中的关键中间体。然而，直接观察它们是难以捉摸的，并且仍然是一个长期存在的挑战。在这里，采用先进的时间分辨电子顺磁共振技术来表征和监测微秒时间尺度上初级氨基催化光氧化还原转化中的关键中间体。首次在光谱和动力学上直接观察到由单电子转移（SET）产生的瞬态烯胺自由基阳离子和α-亚氨基自由基中间体的去质子化形式。在与苯乙烯的反应中，发现烯胺自由基阳离子比α-亚氨基自由基快一个数量级。这揭示了与仲烯胺自由基阳离子相关的去质子化在初级氨基催化的光氧化还原转化中的微妙作用。