Visible-Light-Induced C-H Cyanoalkylation of Azauracils with Cycloketone Oxime Esters via Catalytic EDA Complex

Photoexcitation electron donor-acceptor (EDA) complexes provide an effective approach to produce radicals under mild conditions, while the catalytic version of EDA complex photoactivation remains scarce. Herein, we report a visible-light-induced organophotocatalytic pathway for the cyanoalkylation of azauracils using inexpensive and readily available 1,4-diazabicyclo[2.2.2]octane (DABCO) as a catalytic electron donor. This synthetic method exhibits exceptional compatibility with various functional groups and presents 34 examples in high yields. The efficient cyanoalkylation offers an environmentally friendly and sustainable route toward enhancing the structural and functional diversity of azauracils.

Copper-Catalyzed Radical Relay 1,3-Carbocarbonylation across Two Distinct C═C Bonds

The radical relay provides an effective paradigm for intermolecular assembly to achieve functionalization across remote chemical bonds. Herein, we report the first radical relay 1,3-carbocarbonylation of α-carbonyl alkyl bromides across two separate C═C bonds. The reaction is highly chemo- and regioselective, with two C(sp3)-C(sp3) bonds and one C═O bond formed in a single orchestrated operation. In addition, the synthesis method under mild conditions and using inexpensive copper as the catalyst allows facile access to structurally diverse 1,3-carbocarbonylation products. The plausible mechanism is investigated through a series of control experiments, including radical trapping, radical clock experiments, critical intermediate trapping, and 18O labeling experiment.

Electroreductive Ring-Opening Carboxylation of Cycloketone Oxime Esters with Carbon Dioxide

Electroreductive ring-opening carboxylation of cycloketone oxime esters with atmospheric carbon dioxide is reported. This reaction proceeded under simple constant current conditions in an undivided cell using glassy carbon as the cathode and magnesium as the sacrificial anode, providing substituted γ- and δ-cyanocarboxylic acids in moderate to good yields. Electrochemically generated cyanoalkyl radicals and cyanoalkyl anion are proposed as the key intermediates.

Synthesis of Functionalized Thiazolidin-2-imine and Oxazolidin-2-one Derivatives from p-Quinamines via [3 + 2] Annulation of Isothiocyanates and CO2

An efficient and environmentally friendly synthetic approach to prepare thiazolidine-2-imine and oxazolidine-2-one derivatives has been developed. Thiazolidine-2-imines are synthesized in good to excellent yields by [3 + 2] annulation of p-quinamines with isothiocyanates under catalyst- and solvent-free conditions. Oxazolidine-2-ones are produced in good to excellent yields via [3 + 2] annulation of p-quinamines with CO₂ using triethylenediamine (DABCO) as an organocatalyst. Furthermore, this strategy can be performed on a gram scale and tolerate a wide range of functional groups.

Ni and Fe Catalyzed Cascade Radical Reactions of Oxime Esters with Diselenides

A radical cyclization and ring-opening of oxime esters with diselenides was developed. Both Ni(0) and Fe(II) catalysts could be employed for the selenylation of olefin-containing and cyclic oxime ester derivatives....

Visible-Light-Driven Photoredox-Catalyzed C(sp3)-C(sp3) Cross-Coupling of N-arylamines with Cycloketone Oxime Esters

A novel photoredox-catalyzed C(sp3)-C(sp3) cross-coupling between N-arylamines and cycloketone oxime esters under mild conditions has been accomplished. The redox-neutral reaction proceeds good functional group tolerance and excellent regioselectivity without any...

Oxime ester-enabled anti-Markovnikov hydrosilylation of alkenes

An oxime ester-enabled anti-Markovnikov hydrosilylation of alkenes is developed.

Zn(II)-Functionalized COF as a Recyclable Catalyst for the Sustainable Synthesis of Cyclic Carbonates and Cyclic Carbamates from Atmospheric CO2

A simple covalent organic framework (COF) bearing β-ketoenamine units as a potential heterogeneous ligand for ZnII-catalyzed fixation and transformation of CO2 into value-added chemicals is reported. Catalytic investigations convincingly demonstrated...

Amine-Directed Mizoroki-Heck Arylation of Free Allylamines

The transition metal-catalyzed Mizoroki−Heck reaction is a powerful method to synthesize C–C bonds, allowing access to several important pharmaceuticals. Traditionally free amines have not been compatible with these approaches due...

Palladium-Catalyzed γ,γ'-Diarylation of Free Alkenyl Amines

The direct difunctionalization of alkenes is an effective way to construct multiple C-C bonds in one-pot using a single functional group. The regioselective dicarbofunctionalization of alkenes is therefore an important area of research to rapidly obtain complex organic molecules. Herein, we report a palladium-catalyzed γ,γ'-diarylation of free alkenyl amines through interrupted chain walking for the synthesis of Z-selective alkenyl amines. Notably, while 1,3-dicarbofunctionalization of allyl groups is well precedented, the present disclosure allows 1,3-dicarbofunctionalization of highly substituted allylamines to give highly Z-selective trisubsubstituted olefin products. This cascade reaction operates via an unprotected amine-directed Mizoroki-Heck (MH) pathway featuring a β-hydride elimination to selectively chain walk to furnish a new terminal olefin which then generates the cis-selective alkenyl amines around the sterically crowded allyl moiety. This operationally simple protocol is applicable to a variety of cyclic, branched, and linear secondary and tertiary alkenylamines, and has a broad substrate scope with regard to the arene coupling partner as well. Mechanistic studies have been performed to help elucidate the mechanism, including the presence of a likely unproductive side C-H activation pathway.

Radical Carboxylative Cyclizations and Carboxylations with CO2

Carbon dioxide (CO₂) is not only a greenhouse gas and a common waste product but also an inexpensive, readily available, and renewable carbon resource. It is an important one-carbon (C1) building block in organic synthesis for the construction of valuable compounds. However, its utilization is challenging owing to its thermodynamic stability and kinetic inertness. Although significant progress has been achieved, many limitations remain in this field with regard to the substrate scope, reaction system, and activation strategies.Since 2015, our group has focused on CO₂ utilization in organic synthesis. We are also interested in the vast possibilities of radical chemistry, although the high reactivity of radicals presents challenges in controlling selectivity. We hope to develop highly useful CO₂ transformations involving radicals by achieving a balance of reactivity and selectivity under mild reaction conditions. Over the past 6 years, we along with other experts have disclosed radical-type carboxylative cyclizations and carboxylations using CO₂.We initiated our research by realizing the Cu-catalyzed radical-type oxytrifluoromethylation of allylamines and heteroaryl methylamines to generate valuable 2-oxazolidones with various radical precursors. Apart from Cu catalysis, visible-light photoredox catalysis is also a powerful method to achieve efficient carboxylative cyclization. In these cases, single-electron-oxidation-promoted C-O bond formation between benzylic radicals and carbamates is the key step.Since carboxylic acids exist widely in natural products and bioactive drugs and serve as important bulk chemicals in industry, we realized further visible-light-promoted carboxylations with CO₂ to construct such chemicals. We have achieved the selective umpolung carboxylations of imines, enamides, tetraalkylammonium salts, and oxime esters by successive single-electron-transfer (SSET) reduction. Using this strategy, we have also realized the dearomative arylcarboxylation of indoles with CO₂. In addition to the incorporation of 1 equiv of CO₂ per substrate, we have recently developed a visible-light photoredox-catalyzed dicarboxylation of alkenes, allenes, and (hetero)arenes via SSET reduction, which allows the incorporation of two CO₂ molecules into organic compounds to generate valuable diacids as polymer precursors.In addition to the two-electron activation of CO₂, we sought to develop new strategies to realize efficient and selective transformations via single-electron activation of CO₂. Inspired by the hypothetical electron-transfer mechanism of iron-sulfur proteins, we have realized the visible-light-driven thiocarboxylation of alkenes with CO₂ using catalytic iron salts as promoters. The in-situ-generated Fe/S complexes are likely able to reduce CO₂ to its radical anion, which could react with alkenes to give a stabilized carbon radical. Moreover, we have also disclosed charge-transfer complex (CTC) formation between thiolate and acrylate/styrene to realize the visible-light-driven hydrocarboxylation of alkenes with CO₂ via generation of a CO₂ or alkene radical anion. On the basis of this novel CTC, the visible-light-driven organocatalytic hydrocarboxylation of alkenes with CO₂ has also been realized using a Hantzsch ester as an effective reductant.

Palladium-Catalyzed Regioselective Arylation of Unprotected Allylamines

Palladium-catalyzed organometallic transformations of free amines are often unsuccessful due to side reactions, such as oxidation, that can occur. However, the ability to furnish the free amine products from these reactions is important for improving the utility and sustainability of these processes, especially for accessing their potential as medicinal and agrochemical agents. Notably, the 3,3-diarylallylamine motif is prevalent in a variety of biologically relevant structures, yet there are few catalytic approaches to their synthesis, and none involving the free amine. Herein, we describe a simple protocol for the arylation of cinnamylamines and the diarylation of terminal allylamines to generate a diverse group of 3,3-diarylallylamine products using a PdII precatalyst. Key features of the method are the ability to access relatively mild conditions that facilitate a broad substrate scope as well as direct diarylation of terminal allylamine substrates. In addition, several complex and therapeutically relevant molecules are included to demonstrate the utility of the transformation.

Visible-Light Photoredox-Catalyzed Ring-Opening Carboxylation of Cyclic Oxime Esters with CO2

The carboxylation of cyclic oxime esters with carbon dioxide via visible-light photoredox catalysis is demonstrated for the first time. A variety of cyclic oxime esters undergo ring-opening C-C bond cleavage and carboxylation to give cyanoalkyl-containing carboxylic acids in moderate to good yields. Moreover, this methodology features mild reaction conditions (room temperature, 1 atm), wide substrate scope, good functional group tolerance as well as facile derivations of products. Mechanistic studies indicate that the benzylic radicals and anions might be the key intermediates.

Organic synthesis of fixed CO2 using nitrogen as a nucleophilic center

In this review, recent progress in the application of CO2 as an electrophilic reagent and nitrogen as a nucleophilic center under different catalytic conditions in organic synthesis is summarized. The used catalytic methods in the reactions of CO2 and nitrogen are classified as metal catalysis, metal-free catalysis, photocatalysis and electrocatalysis. Various catalytic conditions have been used to solve the problems of thermodynamic properties and stability of CO2. The transformation mechanisms of these reactions are discussed.