UVA‐Light‐Promoted Catalyst‐Free Photochemical Aerobic Oxidation of Boronic Acids

Abstract

The hydroxy group, and the phenol moiety in particular, is ubiquitous in several natural products, in organic synthesis and/or pharmaceutical industry. With the uprise of photoredox catalysis, many efforts worldwide focus on developing novel and sustainable protocols, providing an easy access to hydroxy‐containing molecules. Boronic acids and boronic ester derivatives are considered valuable precursors for the synthesis of hydroxyl group derivatives. Herein, we report a novel, sustainable, light‐driven protocol, where the impact of wavelength irradiation on boronic acid aerobic photooxidation was examined. In this work, UVA‐light (370 nm) irradiation was found to promote the photocatalyst‐free aerobic oxidation of boronic acids and boronic acid derivatives. Furthermore, a broad scope of substrates was tested and extensive mechanistic studies were performed, in order to probe the reaction mechanism.

Understanding and Controlling Reactivity Patterns of Pd1@C3N4-Catalyzed Suzuki–Miyaura Couplings

“…Besides homocoupling, a slight degradation of 2 to phenol was observed, a pathway that seems to be independent of the presence of 1 (Figure S6), and might be a noncatalytic photodegradation as was previously observed. 50 Further insights into the conversion of 1 could be gathered through 31 P NMR analysis of the reaction mixture after removal of the catalyst (Figure 4c), revealing distinct peaks in three regions. The expected peaks at approximately −5.95 and 29.6 ppm correspond to triphenylphosphine and its oxide, respectively.…”

NPh3-Mediated WO3-Photocatalyzed Semiheterogeneous Hydroxylation of Aryl and Alkyl Boronic Acids

“…Given the abundance and accessibility of organic boronic acid, a series of heterogeneous photocatalyzed oxidative hydroxylation of aryl boronic acids with air (or pure dioxygen) have been established for synthesizing phenols (Scheme a) . Recently, Kokotos and colleagues reported the UVA light-induced photocatalytic hydroxylation of boronic acids in the presence of N , N -diisopropylethylamine (1 equiv) as the base . Argüello’s group developed the visible light CdS–TiO 2 nanohybrid-catalyzed hydroxylation of aryl boronic acids with 1.1 equiv of Et 3 N as the base .…”

“…9 Recently, Kokotos and colleagues reported the UVA lightinduced photocatalytic hydroxylation of boronic acids in the presence of N,N-diisopropylethylamine (1 equiv) as the base. 10 Arguëllo's group developed the visible light CdS−TiO 2 nanohybrid-catalyzed hydroxylation of aryl boronic acids with 1.1 equiv of Et 3 N as the base. 11 Despite the literature protocols being efficient, the development of novel methods for the sustainable hydroxylation of boronic acids is still necessary.…”