Abstract
A metal-free visible-light photoredox-catalyzed intermolecular cyclization reaction of O-2,4-dinitrophenyl oximes to phenanthridines was developed. In this study, the organic dye eosin Y and i-Pr2NEt were used as photocatalyst and terminal reductant, respectively. The oxime substrates were transformed into iminyl radical intermediates by single-electron reduction, which then underwent intermolecular homolytic aromatic substitution (HAS) reactions to give phenanthridine derivatives.
Highlights
Phenanthridine is important substructure found in many naturally occurring alkaloids such as sanguinarine and chelerythrine [1,2,3]
In the context of our study on biological active phenanthridine derivatives [11,29,30,31,32,33,34], we focused our attention on the development of facile, efficient and environmental-friendly synthetic method our attention on the development of facile, efficient and environmental-friendly synthetic method for phenanthridines and related compounds [35,36]
Among theredcommonly available electron-poor O-aryl oximes, O-(2,4-dinitrophenyl) oxime has the highest E1/2 potential value of −0.55 V [27], which is suitable for single electron transfer (SET) with the excited state of the highest E1/2 red potential value of −0.55 V [27], which is suitable for SET with the excited state commonly used photocatalysts such as Ru(bpy)3Cl2.6H2O
Summary
Phenanthridine is important substructure found in many naturally occurring alkaloids such as sanguinarine and chelerythrine [1,2,3]. The intramolecular homolytic aromatic substitution (HAS) reactions of iminyl radicals have shown advantages in the synthesis of phenanthridine derivatives and other N-containing heterocycles. By taking advantage of the single-electron redox potential of a photoexcited catalyst Ir(ppy) , Yu and co-workers [25,26] found that the acyl oximes could be converted to iminyl radical intermediates which were able to undergo intramolecular homolytic aromatic substitution to give phenanthridines (Scheme 1B). Drawing inspiration fromelectron the workreduction of Walton, Yu phenanthridines and Leonori, we and speculated a visible-light photoredox catalyzed single of. Yu and Leonori, we speculated that a visible-light photoredox catalyzed single electron reduction of electron-poor O-phenyl oximes 2 (Scheme 1C) to iminyl radicals might be followed by the generation electron-poor.
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