General Electrochemical Minisci Alkylation of N-Heteroarenes with Alkyl Halides

Herein, we report, for the first time, a general, facile and environmentally friendly Minisci-type alkylation of N-heteroarenes under simple and straightforward electrochemical conditions using widely available alkyl halides as radical precursors. Primary, secondary and tertiary alkyl radicals have shown to be efficiently generated and coupled with a large variety of N-heteroarenes. The method presents a very high functional group tolerance, including various heterocyclic-based natural products, which highlights the robustness of the methodology. This applicability has been further proved in the synthesis of various interesting biologically valuable building blocks. In addition, we have proposed a mechanism based on different proofs and electrochemical evidences.

Radical Addition of Hydroxy Quinazolines and Alkylation of Quinones via the Electro-induced Homolysis of 4-Alkyl-1,4-dihydropyridines

Herein, we report the formation of C(sp3)-centered radicals via the electro-induced homolysis of 4-alkyl-1,4-dihydropyridines (alkyl-DHPs). The resulting alkyl radicals reacted with hydroxy quinazolines or quinones to afford 2-alkyl dihydroquinazolinones or alkylated quinones. A broad range of alkyl DHPs could be used as versatile radical precursors under electrolysis conditions. This alterative strategy provided a simple and effective pathway for the construction of C(sp2)–C(sp3) and C(sp3)–C(sp3) bonds under mild conditions.

NHCs and Visible Light-mediated Photoredox Co-catalyzed Radical 1,2-Dicarbonylation of Alkenes for 1,4-Diketones

Alkenes are ubiquitous, and radical difunctionalization of alkenes represents one of the most practical approaches to constructing value-added compounds. Dicarbonylation of alkenes provides direct access to value-added 1,4-dicarbonyl compounds. However, selectivity control for unsymmetric 1,2-dicarbonylation is an unclosed challenge. We herein describe NHCs and photocatalysis co-catalyzed three competent radical 1,2-dicarbonylation of alkenes by distinguishing two carbonyl groups, providing structurally diversified 1,4-diketones. Mechanistic studies indicated that NHCs-stabilized ketyl-type radicals originate from aroyl fluorides via oxidative quenching process of excited photocatalysis, and acyl radicals are generated from single-electron-oxidation of α-keto acids. Distinct properties of acyl radical and NHCs-stabilized ketyl radical contributed to selectivity control. Transient acyl radicals are rapidly added to alkenes delivering alkyl radicals, which undergo subsequent radical-radical cross-coupling with ketyl-type radicals, affording 1,2-dicarbonylation products. This transformation features mild reaction conditions, broad substruct scope, and excellent selectivity, providing a general and practical approach for the dicarbonylation of olefins.

Photocatalytic Alkylation of α-(Trifluoromethyl)Styrenes with Potassium Xanthogenates

A protocol for the coupling of potassium xanthogenates with α-(trifluoromethyl)styrenes in the presence of triethyl phosphite is reported. The reaction is carried out under blue light irradiation in the presence of organic photocatalyst 3DPAFIPN. The reaction proceeds via formation of alkyl radicals from readily available xanthogenate salts via oxidative desulfurization and cleavage of the carbon–oxygen bond assisted by triethyl phosphite.

Electrochemical C–N bond activation for deaminative reductive coupling of Katritzky salts

Electrosynthesis has received great attention among researchers in both academia and industry as an ideal technique to promote single electron reduction without the use of expensive catalysts. In this work, we report the electrochemical reduction of Katritzky salts to alkyl radicals by sacrificing the easily accessible metal anode. This catalyst and electrolyte free platform has broad applicability to single electron transfer chemistry, including fluoroalkenylation, alkynylation and thiolation. The deaminative functionalization is facilitated by the rapid molecular diffusion across microfluidic channels, demonstrating the practicality that outpaces the conventional electrochemistry setups.

Switchable radical carbonylation by polarity-regulation

Carbonylation reactions involving CO as readily available C1 synthons have become one of the most important tools for construction of carbonyl compounds from feedstock chemicals in modern chemical synthesis. Whereas numerous catalytic methods for carbonylation reactions proceeding via ionic or radical pathways have been reported, an inherent limitation to these methods is the need to control switchable single and double carbonylative formation of value-added products from the same and simple starting materials. Here we describe a new strategy that exploits simple visible-light-driven photoredox catalysis to regulate the polarity of coupling partners to drive switchable radical carbonylation reactions. Controlled trap of various alkyl radicals by single or double CO thereby proceed smoothly with excellent selectivity in the presence of various amine nucleophiles at room temperature, generating valuable amides and α-ketoamides in a versatile and controlled fashion. Combined experimental and DFT computational studies suggest that trap of the initially formed acyl radical by the second molecule of CO to form α-ketoacyl radical is a facile but reversible process; and photoredox-catalyzed SET oxidation of natural nucleophilic amines into relatively electrophilic nitrogen radical cations is responsible for switchable coupling with such two radical intermediates.