Catalytic Aerobic Photo‐oxidation of a Methyl Group on a Heterocycle to Produce an Aldehyde via Homolytic CI Bond Cleavage caused by Irradiation with Visible Light

Abstract

An ew catalytic method was developed for photo-oxidizing the methyl group on aromatic heterocycles such as benzothiazole,b enzoxazole, and quinoline to produce the corresponding aldehyde.T his is the first report of the metal-free catalytic synthesis of benzothiazole-2-carboxaldehydes using molecular oxygen as the terminal oxidant.

An Expanded SET Model Associated with the Functional Hindrance Dominates the Amide-Directed Distal sp3 C–H Functionalization

“…Thermally or photochemically generated radicals inherently exhibit short-lived, high-energetic, and highly reactive characteristics and thus serve as an important class of versatile and highly active species in organic synthesis. − Recent advances in radical chemistry have stimulated considerable interest in exploring new synthetic platforms to enable the challenging radical transformations associated with the elusive rearrangement reactions. − These efforts call for a large-scale renaissance of radical-based methodologies that first emerged with the electrochemical decarboxylation reaction in the 1840s and then underwent a multicentennial period of exploration, eventually leading to an unprecedented prosperity in multiple directions of radical chemistry at the beginning of the 21st century. − , The experimental findings on the radical-mediated approaches show that by employing different additives the radical species can be variously produced in electrolytic, − photolytic, − oxidative − or reductive homolytic, − and transition-metal-based catalytic − or metal-free − systems. Although the used additive is roughly classified as an initiator − or a catalyst − ,− …”

Transition-Metal-Free Oxidation of Benzylic C–H Bonds of Six-Membered N-Heteroaromatic Compounds

“…Recently, significant progress has been made in the copper-catalyzed aerobic oxidation of methyl/methylene of N-heteroaromatic compounds (Scheme , eq 4). − These works are very elegant, while they have some limitations like using relatively higher temperatures and transition metal catalysts. In 2016, Nagasawa and co-workers reported a photo-oxidation of a methyl group on a heteroaromatic compound using molecular oxygen as the terminal oxidant . Although this was a novel job, the method needs a longer reaction time, and there were relatively few quinoline and pyridine substrates involved.…”

“…In 2016, Nagasawa and co-workers reported a photo-oxidation of a methyl group on a heteroaromatic compound using molecular oxygen as the terminal oxidant. 10 Although this was a novel job, the method needs a longer reaction time, and there were relatively few quinoline and pyridine substrates involved. Therefore, further research for developing new methods in this area is still highly required.…”

A Four-Component Reaction for the Synthesis of β-Quinoline Allylic Sulfones under Iron Catalysis

“…As a result, direct quinoline functionalization has attracted considerable interest in organic transformations. Alternatively, 2-methylquinolines frequently serve as a versatile nucleophilic coupling partner (via enamine intermediate), which undergoes nucleophilic addition reaction to construct the new C–C, C–N, and C–O bonds and among others . For example, Huang and co-workers described an nucleophilic addition reaction between 2-alkyl azaarenes and the CN double bonds of N -sulfonyl aldimines .…”