RESUMEN

A reductive (3+2) annulation of lactams through iridium-catalyzed hydrosilylation and photoredox coupling with α-bromoacetic acid was developed. The iridium-catalyzed hydrosilylation of the lactam carbonyl group and subsequent elimination provide a transient cyclic enamine, which undergoes iridium-catalyzed photoredox coupling with α-bromoacetic acid in a one-pot process. The developed conditions show high functional-group tolerance and provide cyclic N,O-acetals containing a quaternary carbon center. The resulting N,O-acetals undergo a variety of acid-mediated nucleophilic addition reactions via iminium ions to give substituted cyclic amines. The developed sequence including reductive (3+2) annulation and acid-mediated nucleophilic addition was successfully applied to the four-step total synthesis of (±)-eburnamonine.

RESUMEN

Alkyl groups are one of the most widely used groups in organic synthesis. Here, a a series of thianthrenium salts have been synthesized that act as reliable alkylation reagents and readily engage in copper-catalyzed Sonogashira reactions to build C(sp3 )-C(sp) bonds under mild photochemical conditions. Diverse alkyl thianthrenium salts, including methyl and disubstituted thianthrenium salts, are employed with great functional breadth, since sensitive Cl, Br, and I atoms, which are poorly tolerated in conventional approaches, are compatible. The generality of the developed alkyl reagents has also been demonstrated in copper-catalyzed Kumada reactions.

RESUMEN

Photocatalytic reactions represent a kind of green and sustainable chemical processes for organic transformations, but the efficiency is limited by the severe recombination and/or inadequate redox potentials of photoinduced charge carriers in photocatalysts. To address these issues, herein, the CdS-EDTA/g-C3N4 heterostructures were designed according to Z-scheme photocatalytic mechanism and synthesized by the hydrothermal growth of CdS on g-C3N4 nanoflakes with assistance of EDTA chelating agent. EDTA played multiple roles in the formation of CdS-EDTA/g-C3N4 heterostructure photocatalysts, such as controlling the morphology of CdS nanostructures, linking CdS and g-C3N4 together, and boosting the charge transfer between two semiconductors. The optimized CdS-EDTA/g-C3N4(10%) photocatalyst exhibited much higher activities toward the selective reduction of nitrophenol and the selective oxidation of benzyl alcohol, than those of CdS/g-C3N4 heterostructures without EDTA. The enhanced photocatalysis of CdS-EDTA/g-C3N4 can be ascribed to the efficient separation and suitable photoredox potentials of photoexcited charge carriers in the EDTA-bridged Z-scheme system. This work provides the inspiration for exploring inexpensive organic electron mediators for constructing all-solid-state Z-scheme photocatalysts and demonstrates the enhanced performance of Z-scheme photocatalysts for photoredox reactions of organic transformations.

RESUMEN

Alkynes are an important class of organic molecules due to their utility as versatile building blocks in synthesis. Although efforts have been devoted to the difunctionalization of alkynes, general and practical strategies for the direct hydroalkylation and alkylarylation of terminal alkynes under mild reaction conditions are less explored. Herein, we report a photoredox/nickel dual-catalyzed anti-Markovnikov-type hydroalkylation of terminal alkynes as well as a one-pot arylalkylation of alkynes with alkyl carboxylic acids and aryl bromides via a three-component cross-coupling. The results indicate that the transformations proceed via a new mechanism involving a single-electron transfer with subsequent energy-transfer activation pathways. Moreover, steady-state and time-resolved fluorescence-spectroscopy measurements, density functional theory (DFT) calculations, and wavefunction analysis have been performed to give an insight into the catalytic cycle.

RESUMEN

The syntheses, properties, and broad utility of noble metal plasmonic nanomaterials are now well-established. To capitalize on this exceptional utility, mitigate its cost, and potentially expand it, non-noble metal plasmonic materials have become a topic of widespread interest. As new plasmonic materials come online, it is important to understand and assess their ability to generate comparable or complementary plasmonic properties to their noble metal counterparts, including as both sensing and photoredox materials. Here, we study plasmon-driven chemistry on degenerately doped copper selenide (Cu2- xSe) nanoparticles. In particular, we observe plasmon-driven dimerization of 4-nitrobenzenethiol to 4,4'-dimercaptoazobenzene on Cu2- xSe surfaces with yields comparable to those observed from noble metal nanoparticles. Overall, our results indicate that doped semiconductor nanoparticles are promising for light-driven chemistry technologies.

RESUMEN

A visible light-promoted protocol for the redox-neutral coupling of N-hydroxyphthalimide esters with different N-heterocyclic compounds is described. The reaction proceeds through an alkyl radical intermediate generated by reductive decarboxylation of N-hydroxyphthalimide esters. In contrast to the original Minisci protocol, polyalkylation can largely be avoided. Mechanistic investigations revealed a radical chain mechanism which in some cases can proceed even if no photocatalyst is added. This valuable and functional group-tolerant reaction produces substituted heterocycles in moderate to excellent yield. The use of inexpensive starting materials and LEDs as the light source are key features of this C-C bond formation.

Asunto(s)

Ésteres/química , Ftalimidas/química , Catálisis , Descarboxilación , Compuestos Heterocíclicos/química , Luz , Estructura Molecular , Procesos Fotoquímicos

RESUMEN

A library of 50 copper-based complexes derived from bisphosphines and diamines was prepared and evaluated in three mechanistically distinct photocatalytic reactions. In all cases, a copper-based catalyst was identified to afford high yields, where new heteroleptic complexes derived from the bisphosphine BINAP displayed high efficiency across all reaction types. Importantly, the evaluation of the library of copper complexes revealed that even when photophysical data is available, it is not always possible to predict which catalyst structure will be efficient or inefficient in a given process, emphasizing the advantages for catalyst structures with high modularity and structural variability.

RESUMEN

A redox-neutral, light-mediated functionalization of unactivated C(sp3 )-H bonds via iminyl radicals is presented here. A 1,5-H transfer followed by the functionalization of a C(sp2 )-H bond takes place in aqueous media producing a variety of elaborated fused ketones. Mechanistic investigations have revealed 1,5-H transfer as the reversible, rate-determining step in this transformation. Divergent scaffolds are also accessible via C(sp3 )-N bond formation upon a careful choice of the reaction additives.

RESUMEN

Photoredox-catalyzed reductive difluoromethylation of electron-deficient alkenes was achieved in one step under tin-free, mild and neutral conditions. This protocol affords a facile method to introduce RCF2 (R=H, Ph, Me, and CH2N3) groups at sites ß to electron-withdrawing groups. It was found that TTMS (tris(trimethylsilyl)silane) served nicely as both the H-atom donor and the electron donor in the catalytic cycle. Experimental and DFT computational results provided evidence that RCF2 (R=H, Ph, Me) radicals are nucleophilic in nature.