Recent Progress in Radical Arylation Reaction with Diaryliodonium Salts under Photocatalysis

Abstract

( a 青岛农业大学化学与药学院 山东青岛 266109.

Photoinduced Alkyl/Aryl Radical Cascade for the Synthesis of Quaternary CF3-Containing Oxindoles and Indoline Alkaloids

“…The arylation–cyclization of N -aryl acrylamides to 3,3-disubstituted oxindoles was typically reported using aryl diazonium salts. , However, due to the thermodynamic instability of aryl diazonium salts, the reaction needs to be carried out at lower temperatures or needs to be prepared in situ . − In this regard, the more stable and easily synthesizable diaryliodonium salts can serve as excellent arylating reagents. , The copper-catalyzed arylation–cyclization of N -aryl acrylamides using diaryliodonium salt is achieved at elevated temperatures . Furthermore, the majority of the light-mediated approaches to generate aryl radicals using diaryliodonium salts require either a photocatalyst or additive. , Therefore, we became interested to examine the feasibility of PC- and additive-free arylation–cyclization cascade reactions between diaryliodonium salts and TFMAM to afford diverse arylated quaternary CF 3 -tethered oxindoles under visible light. Accordingly, we have screened several parameters such as a variety of diaryl iodonium salts with different counter ions, solvents, and light sources to achieve the targeted reaction (see the Supporting Information, Table S1).…”

Synthesis of 3‐(2‐Hydroxyaryl)indazole Derivatives through Radical O‐Arylation and [3,3]‐Rearrangement from N‐Hydroxyindazoles and Diaryliodonium Salts

“…On the basis of our experimental results, a plausible mechanism for the formation of 3 aa and 4 aa from 1 a and 2 a was illustrated in Scheme 3. Initially, Ph⋅ radical and t ‐BuO⋅ radical were generated from diaryliodonium triflate by releasing PhI and − OTf, [17,18] which were reacted with N ‐hydroxyindazole 1 a to afford O‐ arylated intermediate A and dropped t ‐BuOH. A homolysis of N−O bond cleavage provided radical intermediates B and C .…”

“…KOH and K 2 CO 3 delivered 3 aa in 70% and 51% yields, respectively while the reaction did not work using KOAc and pyridine as bases (Table 1, entries 9-12). Next, the effect of temperature was tested (Table 1, entries [13][14][15][16][17][18]. Lowering the temperature to 60 °C or room temperature diminished the yield of 3 aa to 68% and 37%, respectively.…”

“…On the basis of our experimental results, a plausible mechanism for the formation of 3 aa and 4 aa from 1 a and 2 a was illustrated in Scheme 3. Initially, Ph * radical and t-BuO * radical were generated from diaryliodonium triflate by releasing PhI and À OTf, [17,18] which were reacted with…”