Medium and substituent effects on the photochemistry of phenanthridine N-oxides. Is an intermediate of diradical character involved in the photorearrangement of heterocyclic N-oxides?
作者:Angelo Albini、Elisa Fasani、Valeria Frattini
DOI:10.1039/p29880000235
日期:——
The photochemistry of several 6-substituted phenanthridine N-oxides has been investigated, or reinvestigated, in benzene and ethanol. The main processes observed are: (a) 1,2-oxygen and substituent shift to yield N-substituted phenanthridones (2) and (b) ring enlargements to dibenzo[d,f]-1,3-oxazepines (7). With 6-diphenylmethylphenanthridine N-oxide (1b) rearrangement (a) predominates and occurs with
几种6-取代的菲啶N-氧化物的光化学已经在苯和乙醇中进行了研究或重新研究。观察到的主要过程是:(a)1,2-氧和取代基移位以产生N-取代的菲啶酮(2)和(b)扩环成二苯并[ d,f ] -1,3-氧杂氮杂蒽(7)。在6-二苯基甲基菲啶N-氧化物(1b)中,重排(a)占主导地位,苯中的取代基损失为45%(在乙醇中仅为2%)。用6-苯基衍生物(1c)处理(a)在乙醇中占优势,方法(b)在苯中占优势;对于6-对硝基苯基衍生物(1d),后一种方法在两种溶剂中均占优势。用6-氰基菲啶N-氧化物(1e)重排(b)在苯中占优势;在2,3-二甲基丁烯(但不是环己烯)存在下,获得加成产物;用二烯脱氧是主要过程。介质和取代基可能会改变最低激发单重态的性质,但更重要的是会影响沿反应路径发生的双自由基中间体的稳定性,从而促使其趋向于重排(a)或(b))。仅在特定情况下明确指出中间双自由基[从(1b)中消除二苯甲基