Electrochemical Allylic C(sp3)-H Isothiocyanation via [3,3]-Sigmatropic Rearrangement

The direct allylic C(sp3)-H functionalization provides a straightforward protocol for the synthesis of valuable molecules. We report herein the first chemo- and site-selective method for allylic C(sp3)-H isothiocyanation of various internal alkenes under mild electrochemical conditions. This method exhibits broad functional group tolerance and excellent selectivity and can be applied for late-stage isothiocyanation of bioactive molecules. Combined experimental and computational studies indicate that the reaction proceeds via an unexpected [3,3]-sigmatropic rearrangement.

Redox Relay-Induced C-S Radical Cross-Coupling Strategy: Application in Nontraditional Site-Selective Thiocyanation of Quinoxalinones

Oxidative cross-coupling is a powerful strategy to form C-heteroatom bonds. However, oxidative cross-coupling for constructing C-S bond is still a challenge due to sulfur overoxidation and poisoning transition-metal catalysts. Now, electrochemical redox relay using sulfur radicals formed in situ from inorganic sulfur source offers a solution to this problem. Herein, electrochemical redox relay-induced C-S radical cross-coupling of quinoxalinones and ammonium thiocyanate with bromine anion as mediator is presented. The electrochemical redox relay comprised initially the formation of sulfur radical via indirect electrochemical oxidation, simultaneous electrochemical reduction of the imine bond, electro-oxidation-triggered radical coupling involving dearomatization-rearomatization, and the reformation of the imine bond through anodic oxidation. Applying this strategy, various quinoxalinones bearing multifarious electron-deficient/-rich substituents at different positions were well compatible with moderate to excellent yields and good steric hindrance compatibility under constant current conditions in an undivided cell without transition-metal catalysts and additional redox reagents. Synthetic applications of this methodology were demonstrated through gram-scale preparation and follow-up transformation. Notably, such a unique strategy may offer new opportunities for the development of new quinoxalinone-core leads.

Electrochemical Benzylic C-H Amination via N-Aminopyridinium

An electrochemical protocol for benzylic C(sp3)-H aminopyridylation via direct C-H/N-H cross-coupling of alkylarenes with N-aminopyridinium triflate has been developed. This method features excellent site-selectivity, broad substrate scope, redox reagent-free and facile scalability. The generated benzylaminopyridiniums can be readily converted to benzylamines via electroreductive N-N bond cleavage.

Pulsed electrolysis: enhancing primary benzylic C(sp3)-H nucleophilic fluorination

Electrosynthesis is an efficient and powerful tool for the generation of elusive reactive intermediates. The application of alternative electrolysis waveforms provides a new level of control for dynamic redox environments. Herein, we demonstrate that pulsed electrolysis provides a favourable environment for the generation and fluorination of highly unstable primary benzylic cations from C(sp3)-H bonds. By introduction of a toff period, we propose this waveform modulates the electrical double layer to improve mass transport and limit over-oxidation.

Divergent process for the catalytic decarboxylative thiocyanation and isothiocyanation of carboxylic acids promoted by visible light

A divergent photoinduced selective synthesis of thiocyanate and isothiocyanate derivatives from readily available carboxylic acids was developed using N-thiocyanatosaccharin and a catalytic amount of base or acid. This molecular editing strategy allowed the functionalization of bioactive compounds. A mechanism for the transformation was proposed based on control experiments.

Electrochemical Oxidative C-H Amination through a Ritter-Type Reaction

A straightforward strategy for direct benzylic C-H bond amination via an electrochemical Ritter-type reaction is developed. The reaction demonstrates simpler and milder reaction conditions over the existing methods without extra mediator. Moderate to excellent yields up to 94% of the desired amide products were obtained with a broad substrate scope. The removal of the Ac group by a simple step can afford NH-free benzylic amines, providing a suitable approach for the late-stage functionalization of bioactive molecules.

Photoinduced Synthesis of Thiocyanates through Hydrogen Atom Transfer and One-Pot Derivatization to Isothiocyanates

Photoinduced benzylic C-H thiocyanation is described. A series of alkyl thiocyanates were efficiently obtained by using Selectfluor as the oxidant. Moreover, we accomplished the one-pot isothiocyanation following the C-H thiocyanation. The thiocyanates and isothiocyanates were applied to the divergent transformation of pharmaceuticals.