Paired Electrolysis Enabled Trifluoromethylheteroaromatization of Alkenes and Alkyne with Trifluoromethyl Thianthrenium Triflate (TT-CF3+OTf-) as a Bifunctional Reagent

g-C3N4-Based Heterogeneous Photocatalyzed Synthesis and Evaluation of Antitumor Activities of Fluoroalkylated 4H-Pyrido[1,2-a]pyrimidin-4-ones

The first example of heterogeneous photoredox-catalyzed fluoroalkylation of 4H-pyrido[1,2-a]pyrimidin-4-ones has been developed. With low-cost commercial g-C3N4 as the recyclable photocatalyst and cheap sodium fluoroalkyl sulfonates as the fluoroalkyl source, a variety of fluoroalkylated pyridopyrimidinones were constructed in moderate to high yields. The present reaction can be easily scaled up with good efficiency, and the heterogeneous catalytic system can be reused 5 times with a slight loss of catalytic activities. Furthermore, the biological activity of the synthesized compounds was preliminarily investigated.

Electrochemical Synthesis of 2-Amino-1,3-benzoxazines via TBAI-mediated Desulfurative Cyclization of Isothiocyanates and 2-Aminobenzyl Alcohols

An efficient one-step protocol has been developed to access a variety of 2-amino-1,3-benzoxazine derivatives via tetrabutylammonium iodide-mediated electrochemical desulfurative cyclization of isothiocyanates and 2-aminobenzyl alcohols. The reaction proceeds through a cycle involving in situ iodine generation, desulfurative cyclization, and iodide regeneration, efficiently forming intermolecular C-O and C-N bonds and affording 2-amino-1,3-benzoxazines in moderate to excellent yields. The practical utility of this strategy is evidenced by its broad substrate scope, good functional group compatibility, scalability to gram-scale synthesis, and metal- and oxidant-free conditions.

A General Hydrotrifluoromethylation of Unactivated Olefins Enabled by Voltage-Gated Electrosynthesis

Here we present the first successful hydrotrifluoromethylation of unactivated olefins under electrochemical conditions. Commercially available trifluoromethyl thianthrenium salt (TT+-CF3BF4 -, Ep/2=-0.85 V vs Fc/Fc+) undergoes electrochemical reduction to generate CF3 radicals which add to olefins with exclusive chemoselectivity. The resulting carbon centered radical undergoes a second cathodic reduction, instead of a classical HAT process, to generate a carbanion that can be terminated by protonation from solvent. The use of MgBr2 (+0.20 V onset oxidation potential) plays a key role as an enabling sacrificial reductant for the reaction to operate in an undivided cell. Guided by cyclic voltammetry (CV) studies, fine-tuning the solvent system, trifluoromethylating reagent's counteranion and careful selection of redox processes, this work led to the development of a voltage-gated electrosynthesis by pairing two redox processes with a narrow potential difference (ΔE≈1.00 V) allowing the reaction to proceed with two important advances: (a) high reactivity and selectivity towards hydrotrifluoromethylation over undesired dibromination, and (b) an unprecedented functional group tolerance, including aniline, phenols, unprotected alcohol, epoxide, trialkyl amine, and several redox sensitive heterocycles.

Electrochemical trifluoromethylation of alkynes: the unique role of DMSO as a masking auxiliary

Recent advancements in eco-friendly radical fluoroalkylation have substituted traditional two-electron-based reactions. However, the radical trifluoromethylation of terminal alkynes remains a significant challenge, primarily due to the high reactivity of alkenyl radical intermediates, which predominantly engage in reactions other than the desired elimination. In this work, we have developed an electrochemical trifluoromethylation method for terminal alkynes, facilitating the efficient formation of CF3-alkynes. The success of this method centers on the use of DMSO as a "masking auxiliary", which effectively stabilizes the alkenyl radical intermediate, allowing the reaction to proceed smoothly under mild conditions. This approach is supported by extensive experimental and computational studies, which elucidate the unique mechanism and expand the potential applications of radical trifluoromethylation across chemical synthesis.

Photocatalytic difunctionalization of arylalkenes with quinoxalinones and dialkyl dithiophosphoric acids

Here, a photocatalytic three-component reaction between arylalkenes, quinoxalinones and dialkyl dithiophosphoric acids was developed. This protocol allows the simultaneous incorporation of heterocyclic and dithiophosphoryl groups into a single molecule structure efficiently. These functionalities are important precursors in medicinal chemistry.

Visible Light-Induced Radical Cascade Functionalization of Quinoxalin-2(1H)-ones: Three-Component 1,2-Di(hetero)arylation Approach with Styrenes and Thianthrenium Salts

The additive-free visible light-induced three-component 1,2-di(hetero)arylation of styrenes was developed using quinoxalin-2(1H)-ones and thianthrenium salts. The purple visible light excitable quinoxalin-2(1H)-ones were utilized for the single-electron transfer to aryl thianthrenium salts, where the generated aryl radical species underwent the addition cascade to styrenes and quinoxalin-2(1H)-ones. The direct aryl radical addition to quinoxalin-2(1H)-ones also led to the formation of a side product, C3-aryl quinoxalin-2(1H)-ones, capable of a photoredox process to help the formation of 1,2-di(hetero)arylation products.

Photocatalytic synthesis of polyfluoroalkylated dihydropyrazoles and tetrahydropyridazines

A photocatalytic trifluoromethylation/cyclization reaction of N-allyl and N-homoallyl aldehyde hydrazones with trifluoromethyl thianthrenium triflate was developed for the synthesis of trifluoromethylated dihydropyrazoles and tetrahydropyridazines. Besides, PhI(O2CCHF2)2 was employed to realize the construction of difluoromethylated dihydropyrazoles and tetrahydropyridazines. These protocols exhibit a broad substrate scope and good functional group tolerance.

The merger of electro-reduction and hydrogen bonding activation for a radical Smiles rearrangement

The reductive activation of chemical bonds at less negative potentials provides a foundation for high functional group tolerance and selectivity, and it is one of the central topics in organic electrosynthesis. Along this line, we report the design of a dual-activation mode by merging electro-reduction with hydrogen bonding activation. As a proof of principle, the reduction potential of N-phenylpropiolamide was shifted positively by 218 mV. Enabled by this strategy, the radical Smiles rearrangement of N-arylpropiolamides without external radical precursors and prefunctionalization steps was accomplished. [DBU][HOAc], a readily accessible ionic liquid, was exploited for the first time both as a hydrogen bonding donor and as a supporting electrolyte.

Unusual Regio- and Chemoselectivity in Oxidation of Pyrroles and Indoles Enabled by a Thianthrenium Salt Intermediate

A dearomative oxidation of pyrroles to Δ3-pyrrol-2-ones is described, which employs a sulfoxide as oxidant, in conjunction with a carboxylic acid anhydride and a Brønsted acid additive. 3-substituted pyrroles undergo regioselective oxidation to give the product isomer in which oxygen has been introduced at the more hindered position. Regioselectivity is rationalized by a proposed mechanism that proceeds by initial thianthrenium introduction at the less-hindered pyrrole α-position, followed by distal attack of an oxygen nucleophile and subsequent elimination of thianthrene. The same reaction conditions are also able to effect a chemoselective oxidation of indoles to indolin-3-ones and additionally of indolin-3-ones to 2-hydroxyindolin-3-ones. Here again, the regio- and chemoselectivities are rationalized through the intermediacy of a thianthrenium salt.

Visible-Light Photoredox-Catalyzed Difunctionalization of Alkynes with Quinoxalin-2(1H)-Ones, P4S10, and Alcohols

Visible-light photoredox-catalyzed method has been developed for the synthesis of quinoxalin-2(1H)-one-containing vinyl phosphorodithioates via direct difunctionalization of alkynes with quinoxalin-2(1H)-ones, P4S10 and alcohols. This four-component reaction could be carried out under metal-free and mild conditions, affording a number of quinoxalin-2(1H)-one-containing vinyl phosphorodithioates in moderate to good yields with Z-isomers as the major products. Photocatalytic radical mechanism is proposed based on the results of radical trapping and fluorescence quenching experiments.

Redox Reactions of Organic Molecules Using Rotating Magnetic Field and Metal Rods

In recent years, redox reactions have harnessed light or mechanical energy to enable the formation of chemical bonds. We postulated a complementary approach that electromagnetic induction could promote the redox reaction of organic molecules using a rotating magnetic field and metal rods. Here, we report that electromotive force activates the redox-active trifluoromethylating reagents. This magnetoredox system can be applied to the trifluoromethylation of heteroarenes with high regioselectivity and hydrotrifluoromethylation of alkenes without the need for catalysts and organic additives.

Electrochemical quinuclidine-mediated Minisci-type acylation of N-heterocycles with aldehydes

The electro-generation of acyl radicals from both aromatic and aliphatic aldehydes remains an unmet challenge. We provide a solution to this challenge by merging electro-oxidation and a quinuclidine-mediated hydrogen atom transfer strategy. The generation of acyl radicals at decreased applied potentials compared to that of formyl oxidation exhibits excellent functional group compatibility.

Efficient synthesis of SCF3-containing 3-alkenylquinoxalinones via three-component radical cascade reaction

An efficient and practical method for the synthesis of 3-alkenylquinoxalinones containing the SCF3 group has been readily developed through a three-component radical cascade reaction involving quinoxalinones, alkynes and AgSCF3. The reaction was found to be compatible with a variety of substrates and exhibited a high functional group tolerance and complete E-selectivity. The preliminary study suggests the involvement of a SCF3 radical in the transformation.

Paired Electrolysis-Enabled Arylation of Quinoxalin-2(1H)-ones

The first paired electrolysis-enabled arylation of quinoxalin-2(1H)-ones was achieved using cyanoarenes as the arylation reagents. A variety of 3-arylquinoxalin-2(1H)-ones with various important functional groups were obtained in moderate to good yields under metal- and chemical oxidant-free conditions. With a pair of reductive and oxidative processes occurring among the substrates and reaction intermediates, the power consumption can be dramatically reduced.