Selective electrochemical oxidation of aromatic hydrocarbons and preparation of mono/multi-carbonyl compounds

Sustainable Electrochemical Benzylic C-H Oxidation Using MeOH as an Oxygen Source

New methods and strategies for the direct oxidation of benzylic C-H bonds are highly desirable, owing to the importance of ketone motifs in significant organic transformations and the synthesis of valuable molecules, including pharmaceuticals, pesticides, and fine chemicals. Herein, we describe an electrochemical benzylic C-H oxidation strategy for the synthesis of ketones using MeOH as an oxygen source. Inexpensive and safe KBr serves as both an electrolyte and a bromide radical precursor in the reaction. This transformation also offers several advantages such as mild conditions, broad functional group tolerance, and operational simplicity. Mechanistic investigations by control experiments, radical scavenging experiments, electron paramagnetic resonance (EPR), kinetic studies, cyclic voltammetry (CV), and in-situ Fourier transform infrared (FTIR) spectroscopy support a pathway involving the formation and transformation of benzyl methyl ether via hydrogen atom transfer (HAT) and single-electron transfer (SET). The practical application of our strategy is highlighted by the successful synthesis of five pharmaceuticals, namely lenperone, melperone, diphenhydramine, cinnarizine, and flunarizine.

Electrochemical C-H/C-C Bond Oxygenation: A Potential Technology for Plastic Depolymerization

Herein, we provide eco-friendly and safely operated electrocatalytic methods for the selective oxidation directly or with water, air, light, metal catalyst or other mediators serving as the only oxygen supply. Heavy metals, stoichiometric chemical oxidants, or harsh conditions were drawbacks of earlier oxidative cleavage techniques. It has recently come to light that a crucial stage in the deconstruction of plastic waste and the utilization of biomass is the selective activation of inert C(sp3 )-C/H(sp3 ) bonds, which continues to be a significant obstacle in the chemical upcycling of resistant polyolefin waste. An appealing alternative to chemical oxidations using oxygen and catalysts is direct or indirect electrochemical conversion. An essential transition in the chemical and pharmaceutical industries is the electrochemical oxidation of C-H/C-C bonds. In this review, we discuss cutting-edge approaches to chemically recycle commercial plastics and feasible C-C/C-H bonds oxygenation routes for industrial scale-up.

Electrochemical-Induced C-N Bond Formation: A New Method to Synthesis (Z)-Quinazolinone Oximes Using Primary Amines and Quinazolin-4(3H)-one

A novel and highly selective electrochemical method for the synthesis of diverse quinazolinone oximes via direct electrooxidation of primary amines/C(sp2)-H functionalization of oximes has been developed. The reaction is conducted in an undivided cell under constant current conditions and is oxidant-free, open-air, and eco-friendly. Notably, the protocol shows good functional group tolerance, providing versatile quinazolinone oximes in good yields. Moreover, the mechanism is investigated through control experiments and cyclic voltammogram (CV) experiments.

Switchable Direct Oxygenative Arylation of C(sp3)-H Bonds via Electrophotocatalysis

A metal-free electrophotochemical C(sp3)-H arylation was developed under mild conditions. This method enables a switchable synthesis of diaryl alcohols and diaryl alkanes from inactive benzylic carbons. More importantly, a cheap and safe mediator N-chlorosuccinimide (NCS) was developed, which was employed for the hydrogen atom transfer (HAT) process of the benzylic C-H bond. In addition, this active radical was captured and identified by electron paramagnetic resonance (EPR).

NHPI-Mediated Electrochemical α-Oxygenation of Amides to Benzimides

This report describes a mild electrochemical α-oxygenation of a wide range of linear and cyclic benzamides mediated by N-hydroxyphthalimide (NHPI) in an undivided cell using O₂ as the oxygen source and 2,4,6-trimethylpyridine perchlorate as an electrolyte. The radical scavenger experiment and the ¹⁸O labeling experiment were carried out, which indicated the involvement of a radical pathway and suggested O₂ as an oxygen source in the imides, respectively.

Catalyst- and Oxidizing Reagent-Free Electrochemical Benzylic C(sp3)-H Oxidation of Phenol Derivatives

A site-selective electrochemical approach for the benzylic C(sp³)-H oxidation reaction of phenol derivatives along with hydrogen evolution has been developed. The protocol proceeds in an easily available undivided cell at room temperature under catalyst- and oxidizing reagent-free conditions. The corresponding aryl aldehydes and ketones are obtained in satisfactory yields, and the gram-scale synthesis is easy to be carried out.

Remote carbamate-directed site-selective benzylic C–H oxygenation via synergistic copper/TEMPO catalysis at room temperature

A benzylic C(sp3)–H oxygenation with water at room temperature through a ligand- and additive-free synergistic copper/TEMPO-catalysed radical relay pathway and a remote directing strategy is described.