Electrochemical Amidation: Benzoyl Hydrazine/Carbazate and Amine as Coupling Partners

Programmable C-N Bond Formation through Radical-Mediated Chemistry in Plasma-Microdroplet Fusion

Non-thermal plasma discharge produced in the wake of charged microdroplets is found to facilitate catalyst-free radical mediated hydrazine cross-coupling reactions without the use of external light source, heat, precious metal complex, or trapping agents. A plasma-microdroplet fusion platform is utilized for introduction of hydrazine reagent that undergoes homolytic cleavage forming radical intermediate species. The non-thermal plasma discharge that causes the cleavage originates from a chemically etched silica capillary. The coupling of the radical intermediates gives various products. Plasma-microdroplet fusion occurs online in a programmable reaction platform allowing direct process optimization and product validation via mass spectrometry. The platform is applied herein with a variety of hydrazine substrates, enabling i) self-coupling to form secondary amines with identical N-substitutions, ii) cross-coupling to afford secondary amine with different N-substituents, iii) cross-coupling followed by in situ dehydrogenation to give the corresponding aryl-aldimines with two unique N-substitutions, and iv) cascade heterocyclic carbazole derivatives formation. These unique reactions were made possible in the charged microdroplet environment through our ability to program conditions such as reagent concentration (i. e., flow rate), microdroplet reactivity (i. e., presence or absence of plasma), and reaction timescale (i. e., operational mode of the source). The selected program is implemented in a co-axial spray format, which is found to be advantageous over the conventional one-pot single emitter electrospray-based microdroplet reactions.

K2S2O8-Mediated Denitrogenative Formal Transformylation of Amines with Formylhydrazine in Water

A new approach for direct formylation of various amines has been disclosed using a novel formylating agent, formylhydrazine, to afford N-formylamines in significant yields with application in the gram-scale synthesis of chlorothiazide. This transformylation (transfer of a formyl group from hydrazine to amines) occurs via denitrogenation in the presence of K2S2O8 as the exclusive reagent with water as the solvent. Two reaction pathways involving extremely underexplored formyl or hemiaminal radicals have been postulated, which require further investigation.

Electrochemical stereoselective borylation of Morita-Baylis-Hillman adducts to functionalized allylic boronates

Herein, we disclose a highly efficient and facile electrochemical borylation of Morita-Baylis-Hillman adducts without using any metal catalyst. This methodology demonstrates excellent regio- and stereo-selectivity, leading to a wide range of functionalized E-allylic boronates, including derivatives of ibuprofen and menthol. Under mild and straightforward conditions, this redox-neutral reaction, combined with the scalability and synthetic applications of the allylic boronate esters, underscores its potential for a wide range of applications in organic synthesis.

One-Pot Oxidative Amidation of Aldehydes via the Generation of Nitrile Imine Intermediates

A one-pot procedure for the oxidative amidation of aldehydes via the in situ generation of reactive nitrile imine (NI) intermediates has been developed. Distinct from our progenitor processes, mechanistic and control experiments revealed that the NI undergoes rapid oxidation to an acyl diazene species, which then facilitates N-acylation of an amine. A range of substrates have been explored, including application in the synthesis of pharmaceutically relevant compounds.

Electrochemical NaI-mediated one-pot synthesis of guanidines from isothiocyanates via tandem addition-guanylation

In this study, we present an electrochemical approach for the synthesis of guanidines from isothiocyanates and amines in a single reaction vessel. This one-pot operation takes place in aqueous media, utilizing an undivided cell setup with NaI serving as both the electrolyte and mediator. The process involves the in situ generation of thiourea, followed by electrolytic guanylation with amines. Under ambient temperature conditions, we successfully demonstrated the formation of 30 different guanidine compounds, achieving yields ranging from fair to excellent. Furthermore, the synthesis method could be carried out on a gram scale with a good yield. This protocol stands out for its cost-effectiveness, step-economical design, high tolerance towards various functional groups, and environmentally friendly reaction conditions.

Pd/C Catalyzed Dehalogenation of (Hetero)aryls Using Triethyl­silane as Hydrogen Donor

(Hetero)aryl dehalogenation is a classical transformation usually performed using hydrogen gas and a metal supported on carbon, notably palladium (Pd/C). Though efficient, the need for a milder and operationally simple dehalogenation can arise. We found that the combination of Pd/C as catalyst and triethylsilane (TES) as hydrogen donor in THF resulted in a broadly applicable, easy to set up, and scalable debromination and deiodination. Optimization of the reaction showed that 1 mol% of Pd/C and 4 equiv of TES at room temperature were sufficient to obtain full conversion of most synthons of pharmaceutical interest in 4–24 h. The newly found conditions were applied to a large range of aromatic and heteroaromatic substrates, affording the desired targets in good to excellent yields with an exceptional functional group tolerance.

Electrochemical cycloaddition of hydrazones with cyanamide for the synthesis of substituted 5-amine-1,2,4-triazoles

An eco-friendly and efficient electrochemical method for the synthesis of 5-amine-1,2,4-triazole derivatives has been developed by employing hydrazones or in situ generation of hydrazones with cyanamide using KI as the catalyst and electrolyte. This strategy could be smoothly conducted with simple reaction conditions at room temperature without the addition of a chemical oxidant in an undivided cell, and cyanamide has been proven to be of great value in electrosynthesis.

Radical coupling reactions of hydrazines via photochemical and electrochemical strategies

Hydrazines are versatile building blocks in organic synthesis.