Heterocyclic Electrochemistry: Renewable Electricity in the Construction of Heterocycles

Abstract

Numerous applications in the realm of biological exploration and drug synthesis can be found in heterocyclic chemistry, which is a vast subject. Many efforts have been developed to further improve the reaction conditions to access this interesting family to prevent employing hazardous ingredients. In this instance, it has been stated that green and environmentally friendly manufacturing methodologies have been introduced to create N-, S-, and O-heterocycles. It appears to be one of the most promising methods to access these types of compounds avoiding use of stoichiometric amounts of oxidizing/reducing species or precious metal catalysts, in which only catalytic amounts are sufficient, and it represent an ideal way of contributing toward the resource economy. Thus, renewable electricity provides clean electrons (oxidant/reductant) that initiate a reaction cascade via producing reactive intermediates that facilitate in building new bonds for valuable chemical transformations. Moreover, electrochemical activation using metals as catalytic mediators has been identified as a more efficient strategy toward selective functionalization. Thus, indirect electrolysis makes the potential range more practical, and less side reactions can occur. The latest developments in using an electrolytic strategy to create N-, S-, and O-heterocycles are the main topic of this mini review, which was documented over the last five years.

Indirect Electrocatalysis S─N/S─S Bond Construction by Robust Polyoxometalate Based Foams

“…[9] Besides, the interfacial interaction between the electrode and electrocatalysts, a complicated issue that is closely related to performance, can be neglected, thus chemoselectivity, regioselectivity, or stereoselectivity of reactions can be effectively tuned by the precise design of electrocatalysts used in indirect electrolysis. [10] During past years, common indirect electrocatalysts mainly involve homogeneous electrocatalysts, such as N-oxyl radicals, hypervalent iodine species, halides, amines, benzoquinones (DDQ and tetrachlorobenzoquinone), [11][12][13][14] and transition metals, [15] yet the product separation or electrocatalyst recycling are still a daunting challenge due to the homogeneous nature of electrocatalysts. Despite a few works that have reported heterogeneous electrocatalysts (e.g., G-SACs, [16] Mo-based electrocatalysts, [17] and PorCu [18] ), their generally applied powder forms with the inherent disadvantages like the pulverization of sample would still restrict their potential practical applications.…”

A new type of convergent paired electrochemical synthesis of sulfonamides under green and catalyst-free conditions

“…In contrast, in electro-organic synthesis, electrons are used as green and cost-effective reactant, which has advantages such as simplicity, minimizing the production of toxic waste and energy consumption, and being eco-friendly 10 , 20 . Consequently, the demand for using metal catalysts and hazardous oxidants is eliminated 21 – 24 .…”

“…The reactions that are carried out on the counter electrode are usually reduction or oxidation of the solvent, and their task is to consume the electrons produced in the working electrode or to supply the necessary electrons for the working electrode process. Now, if by changing the counter electrode reaction, to the production of the product or helps to produce the final product, the conventional electrosynthesis process has become “ paired electrosynthesis ” 24 , 25 . This method saves energy and time.…”

“…Since in this method one mole of electrons can perform useful reactions in the working and counter electrodes and since the total current efficiency is the sum of the reactions that occur in each electrode, the current efficiency can increase up to 200% when cathodic and anodic processes produce the same product. Useful and complete information about the " paired electrosynthesis " can be obtained from the references 24 , 25 .…”

Ultrasonic Assisted Three Component Synthesis of 3-Cyano-pyridine-2(1H)-ones

“…Over the past decade, significant efforts have been made to modify chemical processes to promote sustainability and environmental improvement. In recent years, numerous approaches, including microwave [1,2], ionic liquids [3], electrosynthesis [4][5][6], mechanochemical [7] and others [8], have been developed for the organic syntheses. Among them, ultrasonication in chemical reactions is also considered as one of the greatest achievements in this scenario [9,10].…”