A promising electro-oxidation of methyl-substituted aromatic compounds to aldehydes in aqueous imidazole ionic liquid solutions

Site-selective electrooxidation of methylarenes to aromatic acetals

“…With the optimized reaction conditions defined, we set out to explore the scope of the electrooxidation of methylarenes. Notably, the site-selectivity was not significantly affected by introducing a phenyl (3), bromo (4), or cyano group (5) at C5, or by varying the substituent on N1 (6-9) or C2 (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) of the C4,C6-dimethylated benzimidazole substrate (Fig. 2).…”

“…The method showed broad compatibility with common functional groups or moieties such as alkyl bromide (7), alkyne (8), alkene (9), ester (15,16), alcohol (17,18), ketone (19), aldehyde (20), Bocprotected amine (21)(22)(23), ketal (24), azido (25), and aromatic heterocycles (12, 13, 26, and 27). Molecular fragments derived from natural products dehydroabietic acid (28) and lithocholic acid (29) were equally well tolerated. On the other hand, siteselective oxidation of the C6-Me group in C5,C6-dimethylated benzimidazoles bearing an aryl substituent at C2 (30-32) could also be achieved.…”

“…As an alternative to chemical oxidation, electrooxidation eliminates the use of stoichiometric chemical oxidants and is attracting increasing interests [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . Notably, electrooxidation of electron-rich toluene derivatives to substituted benzaldehydes has been applied in the industrial production of panisaldehyde and 3,4,5-trimethoxybenzaldehyde [27][28][29] . Despite these accomplishments, the conversion of structurally complex methylarenes, including medicinally relevant benzoheterocycles in particular, has remained synthetically elusive because of selectivity issues and catalyst inhibition by the coordinating heteroatoms 30 We have been interested in electrochemical synthesis of heterocycles 23,31,32 and recently reported intramolecular dehydrogenative cyclization reactions for the preparation of several types of benzoheterocycles [33][34][35][36][37] .…”

Carbon nitride assisted chemoselective C–H bond photo-oxidation of alkylphenolethoxylates in water medium

“…2 The presence of competitive easil y oxidised substituents in a benzyl ring such as electron-dona ti ng -C-OH, -C=O, -O-C, or -NH2 groups complicates achievi ng activation of a more inert C-H bond. Thus, a variety of methods utilizing homogeneous oxidation, 3 photoactive complexes , 4 metal oxide-supported noble metal nanoparticle s, 5 enzymes 6 and electrochemical oxidation in ionic liquids 7 is developed to overcome this obstacle. Many of the existing oxida ti on protocols are complicated and expensive, they often dema nd the presence of toxic oxidants and/or organic solvents, and external heat must be supplied for the reaction to take place .…”

Electrochemical strategies for C–H functionalization and C–N bond formation

“…396 Anodic oxidation of arenes containing alkyl side chains provides aryl radical cations, which can subsequently be further oxidized to afford benzylic cations upon release of a proton, thus presenting a strategy for carrying out benzylic functionalization. 397 Recently, the Stahl group disclosed an alternative approach to benzylic C-H functionalization (Scheme 35). 398,399 The developed concept consisted of employing N-hydroxyphthalimide (NHPI) as a mediator.…”