Phthalocyanine Zinc‐catalyzed Hydroxylation of Aryl Boronic Acids under Visible Light

Abstract

A visible-light-promoted aerobic oxidative hydroxylation of boronic acids using phthalocyanine zinc as an easily available photosensitizer has been developed. It provided a direct access to synthesize aliphatic alcohols and phenols from boronic acids. The advantages of this approach included the low catalyst loading (0.5 mol%), high efficient, the use of O 2 as an oxygen source, wide substrate range, the simple operational process, and mild conditions.

Oxidative Hydroxylation of Aryl Boronic Acid Catalyzed by Co-porphyrin Complexes via Blue-Light Irradiation

“…As the porphyrins absorbed intensely in the Soret region (around 435 nm) and partially in the Q region (around 500−600 nm), we carried out all hydroxylation reactions under blue LED light (435−600 nm) [43,44]. While similar oxidation reactions from phenyl boronic acid to phenol have been reported elsewhere [45][46][47], the toxicity of hydrogen peroxide, longer reaction times (from 24 h to several days) and higher temperatures make them less-efficient reactions and less eco-friendly [48,49]. The protocol developed here using a Co(II)-porphyrin system showed higher yields within 6 h and mild reaction conditions (room temperature and under the atmosphere) and could be used as an environmentally friendly, reusable catalyst for oxidative hydroxylation transformations.…”

Aqueous Phase Photocatalytic Hydroxylation of Arylboronic Acids Using Polyhedral Cu2O Crystals

“…Similar darkening of Cu 2 O rhombic dodecahedra was observed during reaction with 3-thienylboronic acid in water, and no reaction occurred after 6 and 12 h. Lack of reactivity for N-and S-containing heterocyclic boronic acids has been observed before. 18,25 Since arylboronic esters can also be converted to the corresponding phenols, methoxy-and fluoro-substituted arylboronic esters were synthesized first (Table S2). Under the same reaction condition with blue LED illumination for 12 h, 62% of the methoxyphenol product was obtained (Table 6).…”

“…17,24 Phthalocyanine zinc photosensitizers can also work. 25 Ru complex-incorporated metal− organic frameworks (MOFs), as well as Zr-and Sn-based MOFs, also showed light-induced aerobic oxidation of arylboronic acids. 26−28 Covalent organic frameworks (COFs) were also explored for photocatalytic hydroxylation of arylboronic acid derivatives.…”

Recyclable Cu@C3N4-Catalyzed Hydroxylation of Aryl Boronic Acids in Water under Visible Light: Synthesis of Phenols under Ambient Conditions and Room Temperature

“…Visible-light-promoted organic synthesis avoids the use of high-energy UV light, rendering the synthetic methods highly selective and controllable. Therefore, visible-light-mediated synthesis has emerged as a convenient and powerful tool for organic transformations under mild conditions, which is highly promising from the standpoint of the recent environmental sustainability. − Pioneered by Xiao’s group in 2012, the visible-light-promoted oxidative hydroxylation reactions of aryl boronic acids have been proven to be a valuable method for the synthesis of phenols using Ru­(bpy) 3 Cl 2 , methylene blue, rose bengal, 7 H -benzo­[ c ]­thioxanthen-7-one, 2,2-dimethoxy-2-phenylacetophenone, phthalocyanine zinc, and trichloroacetonitrile as photocatalysts or activating reagents, respectively. − However, those reported approaches were generally homogeneous catalytic systems, in which the reuse of catalysts was difficult (Scheme b). On the other hand, heterogeneous catalysts are favored by industry because of their high efficiency and easy recycling.…”