Unexpected hydrazine hydrate-mediated aerobic oxidation of aryl/ heteroaryl boronic acids to phenols in ambient air

Abstract

A general sub-stoichimetric hydrazine hydrate-mediated aerobic oxidative ipso-hydroxylation of aryl/heteroaryl boronic acids to phenols.

Droplet‐based Continuous Flow Synthesis of Palladium Supported on Reduced Graphene Oxide

“…The best‐performing Pd‐RGO catalyst was synthesized using 1 μL of hydrazine (Entry 2). As the amount of hydrazine increased, the reduction of GO proceeded better, but the undegraded hydrazine affected the Suzuki–Miyaura reaction and lowered the yield (Entry 5, 6) . 4‐tert‐Butyl phenylboronic acid was rapidly decomposed by hydrazine to produce 4‐tert‐butyl phenol (see the Figure S1 in supporting information).…”

Recent Advances in Green Synthesis of Functionalized Phenols from Aromatic Boronic Compounds

“…Later, Han and co‐workers reported a hydrazine hydrate‐mediated hydroxylation of boronic acids and boronate ester with poly(ethylene glycol) as the solvent (Scheme c) . The use of air as the sole oxidant makes the process safe and environmentally benign.…”

Photocatalytic hydroxylation of arylboronic acids using continuous flow reactors

“…This symmetrical substrate has two boronic acid functionalities in para-positions where steric interactions are minimised and therefore cannot interfere with the second hydroxylation step. At the previously optimised conditions ( Table 2, entry 8), the reaction gave almost full conversion to hydroquinone (5) and no selectivity to 4-hydroxyphenylboronic acid (4). Further experiments at high pressure, using higher ow rates showed low selectivity to 4.…”

“…3 Since the 1930s, boronic acids have been perceived as potential substrates for the development of alternative hydroxylation routes to phenols. [3][4][5][6] Although direct boronic acid hydroxylation has received attention, it oen requires the use of strong oxidising agents or toxic metal catalysts. 3,[7][8][9][10][11][12][13][14] Recently, a number of alternative methods have been described, based on the generation of superoxide free radical species (O 2 c À ).…”