Merging Photoredox Catalysis with Iron(III) Catalysis: C5‐H Bromination and Iodination of 8‐Aminoquinoline Amides in Water

Abstract

A simple and efficient protocol for the iron(III)‐catalyzed C5 halogenation of 8‐aminoquinoline with potassium halides via a photoredox process was developed, affording desired products in good to excellent yields. This reaction features its mild and green conditions (proceeding in water under air at room temperature). Electronic effect is not obvious in this reaction, and the desired products can be afforded in good to excellent yields regardless of the benzamides possessing electron‐donating groups or electron‐withdrawing groups; comparatively, substrates containing electron‐donating groups result in slightly higher yields of the coupling products than those of electron‐withdrawing groups. Moreover, a gram‐scale bromination reaction was also successfully fulfilled, demonstrating its potential applicable value in organic synthesis.magnified image

Metal‐Free, Oxidant‐Free, Site‐Selective C−H Halogenations to Aminoquinolines at Room Temperature using N‐Halosaccharins

“…Thereafter, many C5 functionalization including halogenation, protocols have been developed. For halogenations, various halogenating sources like copper halides, [12a,e,i,k,l] sodium halides,,, lithium halide, potassium halides,,, N ‐halosuccinimides were employed in the presence of various transition metal (Cu, Pd and Fe) catalysts (Scheme ). Various external oxidants like bisacetoxyiodosobenzene, oxone, Ag 2 CO 3 have also been used to furnish the desired haloquinolines.…”

C–H Functionalization of Aromatic Amides

“…In recent years, photoredox catalysis has attracted more and more attention in the field of chemical synthesis due to its mild reaction conditions, environmental friendliness, safety and reliability. In 2017, the Wu team described a method for the C‐5–H halogenation via coupling of 8‐aminoquinoline with potassium halide under the action of photoredox and Fe(III) catalysts (Scheme ) . The reaction was carried out under mild conditions: room temperature, under air and with water as solvent.…”

PIDA‐Promoted Selective C5 C−H Selenylations of Indolines via Weak Interactions

“…[11] Transition metal catalyst coordinated with the bidentate directing groups to form a cation-radical intermediate which enable coupling reactions with various free radicals, thus overcame the geometrically inaccessible cyclometallations to achieve the distal CÀ H functionalization. [11] Transition metal catalyst coordinated with the bidentate directing groups to form a cation-radical intermediate which enable coupling reactions with various free radicals, thus overcame the geometrically inaccessible cyclometallations to achieve the distal CÀ H functionalization.…”

“…More recently, transition-metal catalysed remote C 5 CÀ H functionalization of quinoline through oxidative radical pathway have been widely explored. [11] Transition metal catalyst coordinated with the bidentate directing groups to form a cation-radical intermediate which enable coupling reactions with various free radicals, thus overcame the geometrically inaccessible cyclometallations to achieve the distal CÀ H functionalization. In this regard, CÀ C and C-heteroatom bonds formations on the C 5 position of 8-aminoquinolinamide derivatives have been widely developed to access diverse functionalized quinoline scaffolds.…”