Visible‐Light‐Promoted Copper‐Catalyzed Regioselective Benzylation of Pyridine N‐Oxides versus Thermal Acylation Reaction with Toluene Derivatives

Abstract

Copper‐catalyzed visible light mediated direct C–H bond benzylation of pyridine N‐oxides with toluene derivatives was accomplished by recent developments in photochemical carbon–carbon bond formation through a photo‐induced bond‐dissociation strategy. This visible light driven protocol has been successfully applied to a broad scope of pyridine N‐oxides and toluene derivatives. Furthermore, preliminary research indicates that the acylation reaction can be carried out under thermal reaction conditions. This protocol provides easy access to 2‐benzyl and 2‐acyl pyridine N‐oxide derivatives in the presence of a copper catalyst.

Decarboxylative C–H Alkylation of Heteroarene N-Oxides by Visible Light/Copper Catalysis

“…On the basis of relevant reports, , including photocatalysis by a copper complex with a bidentate nitrogen ligand , and our experimental results (Table , entries 8, 12, and 13), a plausible mechanism for copper/photocatalytic decarboxylation coupling is proposed as presented in Figure . First, under visible light irradiation, copper complex L n Cu I X enters the photoexcited [L n Cu I X]* A , which reduces hypervalent iodine­(III) carboxylate 1 leading to an alkyl radical (R • ) ,, and L n Cu II X­(O 2 CR) B , through a single-electron transfer (SET) process.…”

Visible‐Light‐Mediated C‐2 Functionalization and Deoxygenative Strategies in Heterocyclic N‐Oxides

“…Besides photocatalyst‐assisted reactions, a visible light driven Cu‐catalyzed C‐2 benzylation of pyridine N ‐oxides 9 with toluene 10 using CuO (catalyst), K 2 S 2 O 8 (oxidant), and MeCN (solvent) was disclosed by Kianmehr and Gholamhosseyni (Scheme 4). [20] Pyridine N ‐oxides with electron‐rich groups delivered better yields than the ones having electron‐deficient groups. The high points of this method are the use of no photocatalyst and the generation of primary benzylic radicals.…”

Modern metal-catalyzed and organocatalytic methods for synthesis of coumarin derivatives: a review

“…Copper-based catalysts can assist in the activation of C(sp)-H, C(sp 2 )-H, and C(sp 3 )-H bonds to produce various forms of new bonds. 101 Early studies proposed that Cu-catalyzed reactions for the synthesis of heterocycles proceed via either a oneelectron electron transfer, a two-electron electron transfer, or a combination of one and two-electron electron transfer processes. 102 Even with the wide and very beneficial applications of second-row metals like palladium, copper still holds its role in organometallic synthesis.…”