Visible-Light-Triggered Synthesis of N-α-Ketoacylated Sulfoximines by Denitrogenative and Oxidative Functionalization of Vinyl Azides

We have introduced a sulfoximidation reaction initiated by visible light between α-phenyl vinyl azides and NH-sulfoximines. The cost-effective and readily accessible hypervalent iodine reagent (PIDA) easily promoted the oxidative sulfoximidation process to afford N-α-ketoacylated sulfoximines in good to high yields, involving the formation of two new C-O bonds and one C-N bond. Additionally, the protocol offers noteworthy advantages, including its metal-free and photocatalyst-free reaction and its broad substrate compatibility.

Ball-milled prepared Fe3O4-FeSAs-NPs@NC catalyst synergistically facilitate the generation of reactive oxygen species for oxidative trifluoromethylation of alkenes

Heterogeneous catalysts have recently regarded as a promising chose for the thermally-driven generation of the reactive oxygen species (ROS) through catalytic reactions with molecular oxygen, which can facilitate this process by specific geometric and electronic structure. However, the oxidative trifluoromethylation of alkenes to α-trifluoromethylated ketones by CF3SO2Na is rarely reported in this system. In this work, we report a one-pot polymerization ball milling strategy to construct precursor, and then pyrolyze it to obtain specific carbon nanotubes matrix with Fe/Fe3O4 nanoparticles and single atoms Fe. Remarkably, the optimized catalyst (Fe3O4-FeSAs-NPs@NC-1) displays excellent catalytic performance, broad substrates and recyclability for this fluorination reaction via radical pathway. Based on characterizations and mechanistic studies, we discover that the coexistence of Fe/Fe3O4 and Fe-Nx not only synergistically facilitates the catalytic efficiency in altering the electronic structure of Fe sites, but also benefits the absorption of O2 and the ability of the thermally-driven generating ROS which can activate CF3SO2Na to CF3 radical. This work offers a method of designing Fe-based catalysts and also opens up a new thermal-heterogeneous catalysis way for the oxidative trifluoromethylation of alkenes.

Iodine-TBHP mediated efficient synthesis of α-ketoamides from vinyl azides and amines under mild conditions

A convenient and practical synthetic approach for α-ketoamides has been developed under mild conditions. The facile synthesis of α-ketoamides has been accomplished using aryl vinyl azides and secondary amines at room temperature. The inexpensive and readily available iodine and TBHP easily promoted the oxidative amidation process to afford diketoamide derivatives in high yields. This method involves the synthesis of ketoamide compounds via sequential C-O and C-N bond formation. Moreover, metal-free and aerobic conditions and wide substrate scope are the notable advantages of this protocol.

Enantioselective Synthesis of Secondary β-Trifluoromethyl Alcohols via Catalytic Asymmetric Reductive Trifluoroalkylation and Diastereoselective Reduction

Fluorinated motifs are frequently encountered in drugs and agrochemicals. Incorporating fluorine-containing motifs in drug candidates for lead optimization in pharmaceutical research and development has emerged as a powerful tool. The construction of molecules that feature a trifluoromethyl (CF₃-) group on a stereogenic carbon has accumulated broad research efforts. Unlike its well-explored, biologically active methyl counterpart, asymmetric construction of β-trifluoromethylated alcohols bearing adjacent stereocenters still remains elusive. Through retrosynthetic analysis, we posited that followed by sequential reduction of carbonyl, the initial construction of chiral α-trifluoromethylated ketones could render the desired product in a facile, one-pot fashion. Herein, we developed the first example of nickel-catalyzed asymmtric reductive cross-coupling trifluoroalkylation of acyl chlorides for enantioselective synthesis of diverse α-trifluoromethylated ketones. The one-pot reduction of these α-trifluoromethylated ketones furnished corresponding alcohols bearing β-CF₃-substituted stereogenic carbons with excellent diastereoselectivity and complete enantioselective retention. High yields/enantioselectivity, mild conditions, and good functional group compatibility are shown in the system. Utilities of the method are also illustrated by applying asymmetric, late-stage trifluoroalkylation of biologically active complex molecules, revealing tremendous potential for development of CF₃-containing chiral drugs.

Multicomponent reactions and photo/electrochemistry join forces: atom economy meets energy efficiency

Visible-light photoredox catalysis has been regarded as an extremely powerful tool in organic chemistry, bringing the spotlight back to radical processes. The versatility of photocatalyzed reactions has already been demonstrated to be effective in providing alternative routes for cross-coupling as well as multicomponent reactions. The photocatalyst allows the generation of high-energy intermediates through light irradiation rather than using highly reactive reagents or harsh reaction conditions. In a similar vein, organic electrochemistry has experienced a fruitful renaissance as a tool for generating reactive intermediates without the need for any catalyst. Such milder approaches pose the basis toward higher selectivity and broader applicability. In photocatalyzed and electrochemical multicomponent reactions, the generation of the radical species acts as a starter of the cascade of events. This allows for diverse reactivity and the use of reagents is usually not covered by classical methods. Owing to the availability of cheaper and more standardized photo- and electrochemical reactors, as well as easily scalable flow-setups, it is not surprising that these two fields have become areas of increased research interest. Keeping these in view, this review is aimed at providing an overview of the synthetic approaches in the design of MCRs involving photoredox catalysis and/or electrochemical activation as a crucial step with particular focus on the choice of the difunctionalized reagent.

Synthesis of 2-monosubstituted indolin-3-ones by cine-substitution of 3-azido-2-methoxyindolines

We report herein the formal cine-substitution/hydrolysis of 3-azidoindole intermediates generated from 3-azido-2-methoxyindolines (AZINs). This protocol enables the introduction of both various carboxylic acid and alcohol into indolin-3-ones at the C2-position,...

H2O2-mediated room temperature synthesis of 2-arylacetophenones from arylhydrazines and vinyl azides in water

An environmentally benign, cost-efficient and practical methodology for the room temperature synthesis of 2-arylacetophenones in water has been discovered. The facile and efficient transformation involves the oxidative radical addition of arylhydrazines with α-aryl vinyl azides in the presence of H₂O₂ (as a radical initiator) and PEG-800 (as a phase-transfer catalyst). From the viewpoint of green chemistry and organic synthesis, the present protocol is of great significance because of using cheap, non-toxic and readily available starting materials and reagents as well as amenability to gram-scale synthesis, which provides an attractive strategy to access 2-arylacetophenones.

Visible light organic photoredox catalytic cascade reactions

Over the past years, impressive progress has been made in the development of organic photoredox catalytic cascade reactions without the participation of expensive and toxic transition metals under visible light irradiation. These transformations highly depend on the in situ generation of various radical species in the photoredox catalytic cycles. Numerous chemically and biomedically valuable building blocks have been synthesized through this efficient and sustainable protocol. In this review, we highlight the recent progress in this blooming area by presenting a series of new catalytic cascade reactions mediated by organic photoredox catalysts and describe their mechanisms and applications which have appeared in the recent literature.

Vinyl Azides as Radical Acceptors in the Vitamin B12-Catalyzed Synthesis of Unsymmetrical Ketones

Vinyl azides are very reactive species and as such are useful building blocks, in particular, in the synthesis of N-heterocycles. They can also serve as precursors of ketones. These form in reactions of vinyl azides with nucleophiles or radicals. We have found, however, that under light irradiation vitamin B12 catalyzes the reaction of vinyl azides with electrophiles to afford unsymmetrical carbonyl compounds in decent yields. Mechanistic studies revealed that alkyl radicals are key intermediates in this transformation.

Excited State Anions in Organic Transformations

Utilizing light is a smart way to fuel chemical transformations as it allows the energy to be selectively focused on certain molecules. Many reactions involving electronically excited species proceed via open-shell intermediates, which offer novel and unique routes to expand the hitherto used synthetic toolbox in organic chemistry. The direct conversion of non-prefunctionalized, less activated compounds is a highly desirable goal to pave the way towards more sustainable and atom-economic chemical processes. Photoexcited closed-shell anions have been shown to reach extreme potentials in single electron transfer reactions and reveal unusual excited-state reactivity. It is, therefore, surprising that their use as a reagent or photocatalyst is limited to a few examples. In this Review, we briefly discuss the characteristics of anionic photochemistry, highlight pioneering work, and show recent progress which has been made by utilizing photoexcited anionic species in organic synthesis.

Scissoring Enaminone C═C Double Bond by Free Radical Process for the Synthesis of α-Trifluoromethyl Ketones with CF3SO2Na

The C═C double bond cleavage on tertiary enaminones, enabling the formation of a new C-CF₃ bond, has been realized as a practical method for the synthesis of α-trifluoromethyl ketones with only the promotion of TBHP and ambient heating. Control experiments support that the reactions proceed via a featured free radical process. The deuterium labeling experiment employing D₂O indicates that water participated in the product formation by donating the hydrogen atom for the newly generated α-C-H bond in the product.

Electrochemical Tandem Fluoroalkylation-Cyclization of Vinyl Azides: Access to Trifluoroethylated and Difluoroethylated N-Heterocycles

A transition-metal- and oxidant-free electrochemical strategy for radical fluoroalkylation of vinyl azides was developed. The reaction was carried out under mild conditions by using inexpensive and bench-stable R_fSO₂Na (R_f = CF₃, CF₂H) as fluorination reagents. Depending on the starting material, both the electrochemical radical cyclization and dearomatization products could be obtained. This method provides a green and safe approach to synthesize fluorinated nitrogen heterocycles.

Synthesis of α-Amidoketones through the Cascade Reaction of Carboxylic Acids with Vinyl Azides under Catalyst-Free Conditions

An efficient synthesis of α-amidoketone derivatives through the cascade reactions of carboxylic acids with vinyl azides is presented. Compared with literature protocols, notable features of this new method include catalyst-free conditions, broad substrate scope, good tolerance of a wide range of functional groups, and high efficiency. In addition, the synthetic potential of this method as a tool for late-stage modification was convincingly manifested by its application in the structural elaborations of a number of carboxylic acid drug molecules.

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

Phenanthrenes and their aza-analogues have important applications in materials science and in medicine. Aim of this review is to collect recent reports describing their synthesis, which make use of radical cyclizations promoted by a visible light-triggered photocatalytic process.

Syntheses of Trifluoroethylated N-Heterocycles from Vinyl Azides and Togni's Reagent Involving 1,n-Hydrogen-Atom Transfer Reactions

2,2,2-Trifluoroethyl-substituted 3-oxazolines, 3-thiazolines, and 5,6-dihydro-2H-1,3-oxazines have been obtained by reacting substituted vinyl azides with a combination of Togni's reagent and substoichiometric amounts of iron(II) chloride. The results of density functional theory calculations support the proposed mechanism involving 1,n-hydrogen-atom transfer reactions.

Indium(III) Catalyzed Reactions of Vinyl Azides and Indoles

Indium trichloride catalyzes the reaction of vinyl azides with unfunctionalized indoles to give vinyl indoles. This is the first example of displacement of the azide group by a carbon nucleophile while preserving the vinyl function. The protocol employs very mild reaction conditions and offers excellent yields of diverse 3-vinyl indoles. It is amenable to gram scale. Access to a library of 3,3'-bis(indolyl)methanes through condensation of vinyl azides with 2 equiv of an indole is demonstrated.

Transition-metal-free radical relay cyclization of vinyl azides with 1,4-dihydropyridines involving a 1,5-hydrogen-atom transfer: access to α-tetralone scaffolds

The remote C(sp³)–H functionalization enabled by a radical-mediated 1,5-hydrogen-atom transfer (HAT) process using vinyl azides and 1,4-dihydropyridines as precursors has been described.

Visible-light-induced aerobic C3–H fluoroalkoxylation of quinoxalin-2(1H)-ones with fluoroalkyl alcohols

A novel and efficient method of visible-light-induced C3–H fluoroalkoxylation of quinoxalin-2(1H)-ones with fluoroalkyl alcohols is developed. This approach uses readily available fluoroalkyl alcohols as fluoroalkoxylation reagents and displays a wide substrate scope, providing the fluoroalkoxylated products in moderate to good yields. Compared with the previous method, such a transformation uses oxygen as an oxidant, which avoids the utilization of plenty of PhI(TFA)₂. In addition, this strategy also gives a practical tool for the rapid synthesis of histamine-4 receptor antagonist and new N-containing bidentate ligands. A radical mechanism was suggested according to the results of control experiments.

A visible-light-induced aerobic C3–H fluoroalkoxylation of quinoxalin-2(1H)-ones with fluoroalkyl alcohols was reported, providing a green access to fluoroalkoxylated quinoxalin-2(1H)-ones.

Electrochemical trifluoromethylation/semipinacol rearrangement sequences of alkenyl alcohols: synthesis of β-CF3-substituted ketones

Electrochemical oxidative radical trifluoromethylation/semipinacol rearrangement sequences of alkenyl alcohols were developed in this study. This approach is environmentally benign and uses the shelf-stable Langlois reagent as a trifluoromethyl radical precursor and electrons as the oxidizing reagents. The present protocol offers a facile route to prepare β-trifluoromethylated ketone derivatives.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

Metal-Free Visible-Light-Promoted Trifluoromethylation of Vinylcyclopropanes Using Pyrylium Salt as a Photoredox Catalyst

Visible-light-induced metal-free trifluoromethylation of activated, carbocyclic, and unactivated vinylcyclopropanes via a ring-opening reaction using the Langlois reagent (CF₃SO₂Na) is reported to synthesize allylic trifluoromethylated derivatives. Allylic trifluoromethylation was achieved by a photo-oxidative single electron transfer (SET) process at an ambient temperature and under metal-free conditions and visible-light irradiation using pyrylium salt as a photoredox catalyst. The reported methodology has an operational simplicity, broad substrate scope, high functional group tolerance, and scalability.

Radical alkylation of para-quinone methides with 4-substituted Hantzsch esters/nitriles via organic photoredox catalysis

A novel photocatalytic protocol is herein described for the preparation of functionalized phenols via radical alkylation of para-quinone methides under transition-metal-free conditions. The reaction is external oxidant free and performed at ambient temperature upon visible light irradiation, allowing the access to various desired products in satisfactory yields. The readily available 4-alkyl-1,4-dihydropyridines serve as the effective alkyl radical precursors.

Cross coupling of alkylsilicates with acyl chlorides via photoredox/nickel dual catalysis: a new synthesis method for ketones

Photoredox/nickel dual catalysis using silicates and acyl chlorides allows a new method of formation of ketones. Flow chemistry can be applied.