Dual Photoredox/Gold Catalysis Arylative Cyclization of o-Alkynylphenols with Aryldiazonium Salts: A Flexible Synthesis of Benzofurans

Abstract

A new method for the arylative cyclization of o-alkynylphenols with aryldiazonium salts via dual photoredox/gold catalysis is described. The reaction proceeds smoothly at room temperature in the absence of base and/or additives and offers an efficient approach to benzofuran derivatives. The scope of the transformation is wide, and the limitations are discussed. The reaction is proposed to proceed through a photoredox-promoted generation of a vinylgold(III) intermediate that undergoes reductive elimination to provide the heterocyclic coupling adduct.

Light‐Induced Mechanistic Divergence in Gold(I) Catalysis: Revisiting the Reactivity of Diazonium Salts

“…In these transformations diazonium salts commonly serve as aryl donors, leading to the extrusion of N 2 (for representative examples see Scheme A) . In 2016 the group of Fensterbank reported the synthesis of arylated benzofurans from o ‐alkynylphenols combining a photo(redox) catalyst (Ru(bpy) 3 (PF 6 ) 2 ) and a Au catalyst . This reaction interested us in two ways: 1) Some of us recently reported reactions involving diazonium salts that did not require a photo(redox) catalyst and wondered if this reaction could also be carried out in the absence of an additional photo(redox) catalyst.…”

Gold‐Catalyzed Cross‐Coupling Reactions: An Overview of Design Strategies, Mechanistic Studies, and Applications

“…Ad omino bis-arylatives equence preceded an initial C(sp 2 )ÀC(sp) cross-coupling. [272] The yield and regioselectivity of the products depended critically on the presence of the electron-donating or electron-withdrawing groups present on the alkyne and/ort he aryl diazonium salt. [270] Concurrently,Y ee tal.…”

“…Dual Au and photoredox catalyzedC ÀCcross-coupling of alkynes with aryl diazonium salts throughanarylative version of the Meyer-Schuster rearrangement, studied by (a) Gloriuse tal., [266] (b) Alcaide et al, [267] and (c) Shin et al [268] Scheme52. Dual Au and photoredox catalyzedintramolecular( a) alkoxyarylation, [272] (b) amino-arylation, [273] and (c) ipso-arylation-cyclization [274] reactions of alkynes with aryl diazonium salts. Dual Au and photoredox catalyzedintramolecular( a) alkoxyarylation, [272] (b) amino-arylation, [273] and (c) ipso-arylation-cyclization [274] reactions of alkynes with aryl diazonium salts.…”

Visible Light‐Catalyzed Decarboxylative Alkynylation of Arenediazonium Salts with Alkynyl Carboxylic Acids: Direct Access to Aryl Alkynes by Organic Photoredox Catalysis

“…In contrast, other cyclic iodine(III) reagents methoxybenziodoxole (BI-OMe) and acetoxybenziodoxole (BI-OAc) gave even better results, while the reactivity with BI-OAc was the best ( Table 1, entries 3 and 4). Further control experiment indicated that no reaction took place in the absence of light, which clearly showed that the light irradiation was necessary for this transformation ( [22][23]. The metal complexes ([Ru(bpy) 3 ] 2 + , fac-[Ir(ppy) 3 ]) and organic dyes (Rhodamine B, rose bengal) have been explored (Table 1, entries 5-9).…”

“…The reaction of arenediazonium salts with internal/terminal alkynes usually through visible light-induced radical-triggered chemoselective domino process to access ketones/heterocycle (Scheme 2). [22] König et al first reported the photocatalytic reaction of o-methylthio-arenediazonium salts with alkynes yields substituted benzothiophenes (Scheme 2, D). [21] Ollivier's and Alcaide's group independently developed dual photoredox/gold catalysis arylative cyclization of ortho-alkynylphenols/ 2-[(trimethylsilyl)ethynyl]phenol with aryl diazonium salts as flexible synthesis of benzofurans, although with different selectivity (Scheme 2, B and C).…”