Reusable, homogeneous water soluble photoredox catalyzed oxidative dehydrogenation of N-heterocycles in a biphasic system: application to the synthesis of biologically active natural products

Abstract

Herein, a simple and efficient method for the oxidative dehydrogenation (ODH) of tetrahydro-β-carbolines, indolines and (iso)quinolines is described using a reusable, homogeneous cobalt-phthalocyanine photoredox catalyst in a biphasic medium.

Catalytic oxidative dehydrogenation of N-heterocycles with nitrogen/phosphorus co-doped porous carbon materials

“…In general, oxidative dehydrogenations of saturated and partially saturated heterocycles offer an efficient and straightforward route for the synthesis of functionalized aromatic Nheterocycles. [1][2][3][4][5][6][7] As an example (iso)quinolines are of interest for many applications including dyes, paints, solvents, and corrosion inhibitors (Scheme 1A). 8,9 In addition, many of these and related N-heterocycles are important building blocks for bioactive molecules and natural products, including pharmaceuticals and agrochemicals, such as anti-schizophrenia drug 10 and coccidiostats.…”

Photocatalytic Aerobic Dehydrogenation of N-Heterocycles with Ir(III) Photosensitizers Bearing the 2(2′-Pyridyl)benzimidazole Scaffold

“…In particular, the synthesis of a variety of N-heteroarenes (quinolines, quinoxalines, quinazolines, acridines, and indoles) has been performed using this type of strategy in the presence of different photocatalytic systems: [Ru(bpy) 3 ]Cl 2 , 17 Rose Bengal, 9 TiO 2 grafted with Ni(II) ions in the presence of 4-amino-TEMPO, 18 and a cobalt-phthalocyanine photoredox catalyst in a biphasic medium. 19 Nevertheless, there is still scope to explore new photosensitizers with the goal of increasing product yields, reducing reaction times and employing solvents with low boiling points. What is more, additional studies should be done for a better understanding of the reaction mechanism entailed in this type of transformations.…”

“…Alternatively, it is possible to access N-heteroarenes through oxidative dehydrogenation (ODH) of partially saturated precursors under aerobic photocatalytic conditions, which implies the use of O 2 as the hydrogen acceptor (green oxidant), visible light, and a photosensitizer. In particular, the synthesis of a variety of N-heteroarenes (quinolines, quinoxalines, quinazolines, acridines, and indoles) has been performed using this type of strategy in the presence of different photocatalytic systems: [Ru­(bpy) 3 ]­Cl 2 , Rose Bengal, TiO 2 grafted with Ni­(II) ions in the presence of 4-amino-TEMPO, and a cobalt-phthalocyanine photoredox catalyst in a biphasic medium . Nevertheless, there is still scope to explore new photosensitizers with the goal of increasing product yields, reducing reaction times and employing solvents with low boiling points.…”

Cobalt nanoparticles supported on microporous nitrogen-doped carbon for an efficient catalytic transfer hydrogenation reaction between nitroarenes and N-heterocycles

“…To date, the independent synthesis of either arylamines or unsaturated N-heterocycles has been extensively studied, 1,2 such as the reduction of nitroaromatic compounds to arylamines using high-pressure H 2 as a reductant 3,4 and oxidative dehydrogenation of saturated N-heterocycles to quinolines and indoles with excessive oxidants such as TBHP, sulfur, SeO 2 , 2-iodoxybenzoic acid (IBX), 2,3-dichloro-5,6-dicyano-1,4benzoquinone (DDQ), and O 2 . [5][6][7] If separately conducted, the two above-mentioned reactions require additional reagents and are often proceeded under harsh conditions, 8 which complicates the catalytic systems and increases overall costs (Scheme 1a).…”