Visible-Light Photoredox Borylation of Aryl Halides and Subsequent Aerobic Oxidative Hydroxylation

Abstract

Efficient and practical visible-light photoredox borylation of aryl halides and subsequent aerobic oxidative hydroxylation were developed. The protocols use readily available aryl halides and bis(pinacolato)diboron as the starting materials, fac-Ir(ppy) as the photocatalyst, and corresponding arylboronic esters and phenols were obtained in good yields. The methods show some advantages including simple equipment, mild conditions, easy operation, and wide substrate scope. Therefore, they should provide a valuable strategy for chemical transformations.

Metal‐Free Radical Borylation of Alkyl and Aryl Iodides

“…[6] However,a ll these valuable methods require at ransition metal catalyst, al igand and as toichiometric amount of ab ase.T oo ur knowledge,m etal and additive-free radical borylation of alkyl halides with diborons is unknown. [7] Arylboronates can be obtained from haloarenes and diborons via reactive aryl radicals [8][9][10][11][12][13] (Scheme 1B). Along these lines,Marder developed azinc(II)-catalyzed borylation of aryl halides using astoichiometric base [8] and photoinduced aryl halide borylation was reported by Larionov, [9] Li [10] and Fu.…”

“…Along these lines,Marder developed azinc(II)-catalyzed borylation of aryl halides using astoichiometric base [8] and photoinduced aryl halide borylation was reported by Larionov, [9] Li [10] and Fu. [11] Recently,apyridine-catalyzed radical borylation of aryl halides was disclosed by Jiao. [12] We present herein mild radical borylation of both alkyl and aryl iodides with commercial bis(catecholato)diboron as the boron source (Scheme 1C).…”

Photocascade Catalysis: A New Strategy for Cascade Reactions

“…Visible‐light photoredox catalysis has also been established as a powerful procedure for aryl C−X bonds (X=I, Cl, Br) cleavage by a SET reduction process, and enables diverse C−C bond‐forming transformations. On the basis of this strategy and the photoredox‐catalyzed oxidation of boronic acids reported by the authors of this paper, the group of Fu recently disclosed a visible‐light photocascade catalytic one‐pot borylation of aryl halides and hydroxylation of the initially formed arylboronic esters to give valuable phenols . In this process, both of the key intermediates, aryl radicals and superoxide radical anion, are formed by SET reduction.…”

Decarboxylative Borylation: New Avenues for the Preparation of Organoboron Compounds

“…Aryl radicals could be generated from arylamine derivatives, aryldiazonium salts, aryl halides, or aryl triflates, which would then interact with borylating reagents to afford the borylated products. In contrast, far less attention has been paid to the synthesis of alkyl boronic derivatives through the intermediary of alkyl radicals: only three examples of borylation from alkyl bromides were disclosed by the Fu group in 2016, in what was an additional application of their visible‐light photoredox methodology for borylation of aryl halides.…”