Bifunctional reactivity of the nitrophenoxyl group in intramolecular photoreactions
作者:Kiyoshi Mutai、Hideyuki Tukada、Ryoichi Nakagaki
DOI:10.1021/jo00016a017
日期:1991.8
The photochemical behavior of a homologous series of compounds, p-O2NC6H4O(CH2)(n)NHPh (n = 2-10, 12, and 16) in acetonitrile is reported. The lower (n = 2-6) homologues undergo an apparently nucleophilic type rearrangement to give omega-((p-nitrophenyl)amino)alkanol, while the higher homologues (n greater-than-or-equal-to 8) undergo an intramolecular photoredox reaction accompanied by C-N bond cleavage to give omega-(p-nitrosophenoxy)alkanal and aniline. The n = 7 homologue is situated at the switching point of these two reaction pathways, exhibiting neither type of photoreactions. Photoinduced intramolecular electron transfer to generate a radical ion pair is observed for all homologues, and the quantum yield decreases with increasing chain length. This species is the intermediate in the photorearrangement, for which the effect of base-catalysis is discussed in connection with the reaction mechanism. Comparison of the quantum yield for the electron transfer in 1 with that in 1-(anilinomethyl)-4-((p-nitrophenoxy)methyl)cyclohexane reveals the dominance of through-bond electron-transfer mechanism in the higher (n greater-than-or-equal-to 6) homologues. The reaction quantum yield vs chain length profile is discussed in terms of the relative quantum yield of the radical ion pair, the chain conformation, and the photoredox reaction mechanism.