Visible‐Light‐Driven Synthesis of Phenanthridin‐6(5H)‐one and N‐Substituted Carbazole Derivatives through Intramolecular C‐H Arylation

The synthesis of phenanthridinones and carbazoles by intramolecular photo- and Base-promoted Homolityc Aromatic Substitution photo-BHAS) reaction from N-(2-halobenzyl)-N-methylanilines or N-substituted-N-phenyl anilines is presented. The synthetic protocol uses only KO ^t Bu and DMSO to generate aryl radicals under visible-light irradiation. An exciplex complex between the substrates and the dimsyl anion could be involved in the initiation step.

Abstract

A visible-light-driven approach towards phenanthridin-6(5H)-one and carbazole rings synthesis under transition-metal-free conditions is here reported. Phenanthridinones and carbazoles are synthesized through an intramolecular arylation of the corresponding N-(2-halobenzyl)-N-methylanilines or N-substituted-N-phenyl anilines using KO ^t Bu as base in dimethyl sulfoxide (DMSO) at room temperature (rt), employing blue light emitting diodes (LEDs) as the light source. The reaction proceeds through photo- and base-promoted homolytic aromatic substitution via photoinduced electron transfer mechanism and it exhibits good tolerance to different functional groups, resulting in good to very good yields (up to 86 %).

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