Photocatalyst‐free, Visible Light Driven, Gold Promoted Suzuki Synthesis of (Hetero)biaryls

Abstract

A visible‐light driven Suzuki cross‐coupling reaction was performed with colored and bench‐stable arylazosulfones in the presence of Ph3PAuCl (5 mol %) as the catalyst. The absence of a photocatalyst, along with the use of commercially available and easy‐to‐handle arylboronic acids underline the novelty and synthetic usefulness of the protocol. A reaction mechanism involving the generation of an aryl radical as the key intermediate has been proposed on the basis of experimental investigations.

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

“…Then, the alkyne substrate is activated by the Au III intermediate. [290] Chem. The catalytic cycle is similart othat proposed earlierf or the dual Au and photoredox catalysis occurring in the presenceo faphotocatalyst.S auer et al in another study, reported photosensitizer-free, Au-and photoredox-mediated Suzuki cross-coupling reactions between aryl boronic acids and aryl diazonium salts (Scheme 58 a).…”

“…(a) Dual Au and visible-light-promoted Suzuki coupling reaction for the selective synthesis of hetero-biaryls. [290] Chem. Eur.J.2020, 26, www.chemeurj.org 2019 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim state.…”

Homogeneous Gold-Catalyzed Aryl–Aryl Coupling Reactions

“…As an alternative to aryldiazonium salts, Protto and Bandini et al have developed a cross-coupling reaction between arylboronic acids and arylazosulfones that takes place under photocatalyst-free conditions (Scheme 21). 38 Under light irradiation, the photolabile arylazosulfones fragment into an aryl radical and a methanesulfonyl radical. The authors propose that after addition of the aryl radical to gold(I), the generated gold(II) intermediate is oxidized to gold(III) by the methanesulfonyl radical.…”

Hydro/Deutero Deamination of Arylazo Sulfones under Metal- and (Photo)Catalyst-Free Conditions

“…Indeed, the irradiation with visible light of an arylazo sulfone in polar solvents resulted in the homolytic cleavage of the S–N bond, with the subsequent formation of the corresponding aryl radical. Such behavior has been exploited in the preparation of aromatic amides [38], allylarenes [39], triarylethylenes [40], as well as in the photocatalyst-free, gold catalyzed Suzuki coupling to biaryls [41]. We reasoned that such substrates could be employed in the development of a photocatalyst-free, visible-light driven hydro/deutero deamination process exploiting the well-known hydrogen atom abstraction capability of aryl radicals (Ar • , Scheme 1d), as detailed below.…”