Chlorophyll-Catalyzed Visible-Light-Mediated Synthesis of Tetrahydroquinolines from N,N-Dimethylanilines and Maleimides

Abstract

Natural pigment chlorophyll was used as a green photosensitizer for the first time in a visible-light photoredox catalysis for the efficient synthesis of tetrahydroquinolines from N,N-dimethylanilines and maleimides in an air atmosphere. The reaction involves direct cyclization via an sp C-H bond functionalization process to afford products in moderate to high yields (61-98%) from a wide range of substrates with a low loading of chlorophyll under mild conditions. This work demonstrates the potential benefits of chlorophyll as photosensitizer in visible light catalysis.

Construction of N‐Heterocycles through Cyclization of Tertiary Amines

“…Later, this type of cyclization reaction was extensively investigated by several research groups . Amongst these approaches, the implementation of these cyclization reactions under visible‐light photoredox catalysis conditions by using various photosensitizers was feasible . Enabled by merging a [Ru(bpy) 3 ]Cl 2 photocatalyst and a cobaloxime catalyst, Wu and co‐workers further developed this reaction in a new perspective (Scheme ) .…”

“…[69][70][71][72][73][74][75] Amongst these approaches, the implementation of thesec yclization reactions under visible-light photoredox catalysis conditions by using variousp hotosensitizers was feasible. [71][72][73][74][75] Enabled by merging a[ Ru(bpy) 3 ]Cl 2 photocatalyst and ac obaloxime catalyst, Wu and co-workersf urtherd eveloped this reaction in an ew perspective( Scheme 32). [76] In this transformation, an external oxidant is not necessary anymore and maleimides act as hydrogen acceptors.…”

Visible light mediated cyclization of tertiary anilines with maleimides using a supported iridium complex catalyst

“…[10][11][12] The cyclization of tertiary anilines and maleimides was the typical visible light mediated reaction, in which the inert C-H bond interacted with a vinyl group to form the cyclic product in one step. [13][14][15][16][17][18][19][20][21][22][23] This transformation could be realized by using Ru(bpy) 3 Cl 2 13 or Ir(ppy) 2 (dtbbpy)PF 6 13 or [Cu(dap) 2 ]Cl 16 as a photocatalyst. However these transition metal complexes suffer from the drawbacks of high cost, difficult recovery and an inability to be reused.…”

“…We wondered whether these cyclization reactions can be achieved in a more environmentally benign way with an inexpensive heterogeneous catalyst that can easily be isolated aer the reaction. [23][24][25][26][27] Recently much attention was taken on implementing visible-light photoredox catalysis with heterogeneous catalysts. TiO 2 and related semiconductors are used as the common heterogeneous photocatalysts.…”

Photosynthesis-inspired H2 generation using a chlorophyll-loaded liposomal nanoplatform to detect and scavenge excess ROS

“…Figure 2 presents a potential mechanism of the photocatalytic evolution of hydrogen. When red UCL at 660 nm is harvested by Chla (a photosensitizer), the latter becomes excited (Chla*) [17][18][19] . The photo-excited electrons that are released from the Chla* are rapidly transferred to the AuNPs (an electron acceptor and a proton-reducing catalyst) that are conjugated with the Cit-UCNP.…”