Copper Photoredox Catalyzed A3’ Coupling of Arylamines, Terminal Alkynes, and Alcohols through a Hydrogen Atom Transfer Process

Synthesis of Ketonylated Carbocycles via Excited-State Copper-Catalyzed Radical Carbo-Aroylation of Unactivated Alkenes

Carbocycles are core skeletons in natural and synthetic organic compounds possessing a wide diversity of important biological activities. Herein, we report the development of an excited-state copper-catalyzed radical carbo-aroylation of unactivated alkenes to synthesize ketonylated tetralins, di- and tetrahydrophenanthrenes, and cyclopentane derivatives. The reaction is operationally simple and features mild reaction conditions that tolerate a broad range of functional groups. Preliminary mechanistic studies suggest a reaction pathway beginning with photoexcitation of [CuI-BINAP]2 and followed by a single electron transfer (SET), radical aroylation of unactivated alkenes, radical cyclization, and re-aromatization, affording the desired ketonylated carbocycles.

Excited-State Copper Catalysis for the Synthesis of Heterocycles

Heterocycles are one of the largest groups of organic moieties with significant medicinal, chemical, and industrial applications. Herein, we report the discovery and development of visible-light-induced, synergistic excited-state copper catalysis using a combination of Cu(IPr)I as a catalyst and rac-BINAP as a ligand, which produces more than 10 distinct classes of heterocycles. The reaction tolerates a broad array of functional groups and complex molecular scaffolds, including derivatives of peptides, natural products, and marketed drugs. Preliminary mechanistic investigation suggests in situ generations of [Cu(BINAP)₂ ]⁺ and [Cu(IPr)₂ ]⁺ catalysts that work cooperatively under visible-light irradiation to facilitate catalytic carbo-aroylation of unactivated alkenes, affording a wide range of useful heterocycles.

Cu2 O Nanocrystals-Catalyzed Photoredox Sonogashira Coupling of Terminal Alkynes and Arylhalides Enhanced by CO2

Herein the first visible-light-activated Sonogashira C-C coupling reaction at room temperature catalyzed by single-metal heterogeneous Cu₂ O truncated nanocubes (Cu₂ O TNCs) was developed. A wide variety of aryl halides and terminal alkynes worked well in this recyclable heterogeneous photochemical process to form the corresponding Sonogashira C-C coupling products in good yields. Mechanistic control studies indicated that CO₂ enhances the formation of light-absorbing heterogeneous surface-bound Cu^I -phenylacetylide (λ_max =472 nm), which further undergoes single-electron transfer with aryl iodides/bromides to enable Sonogashira C sp 2 -C_sp bond formation. In contrast to literature-reported bimetallic TiO₂ -containing nanoparticles as photocatalyst, this work avoided the need of cocatalysis by TiO₂ . Single-metal Cu^I in Cu₂ O TNCs was solely responsible for the observed C sp 2 -C_sp coupling reactions under CO₂ atmosphere.

Redox-Active Guanidines in Proton-Coupled Electron-Transfer Reactions: Real Alternatives to Benzoquinones?

Guanidino-functionalized aromatics (GFAs) are readily available, stable organic redox-active compounds. In this work we apply one particular GFA compound, 1,2,4,5-tetrakis(tetramethylguanidino)benzene, in its oxidized form in a variety of oxidation/oxidative coupling reactions to demonstrate the scope of its proton-coupled electron transfer (PCET) reactivity. Addition of an excess of acid boosts its oxidation power, enabling the oxidative coupling of substrates with redox potentials of at least +0.77 V vs. Fc⁺ /Fc. The green recyclability by catalytic re-oxidation with dioxygen is also shown. Finally, a direct comparison indicates that GFAs are real alternatives to toxic halo- or cyano-substituted benzoquinones.