Site-Selective, Photocatalytic Vinylogous Amidation of Enones

Site-Selective γ-Trihalomethylation and γ-Dihalomethylidenation of Silyl Dienol Ethers under Organophotoredox Catalysis

We report a general remote tribromo- and trichloromethylation process using CBr4 and CBrCl3 as ready available sources of trihalomethyl radicals. This method operates under mild and metal-free photocatalyzed conditions and enables the access to γ-trihalomethylated enals with complete regioselectivity in up to 71 % isolated yield. Importantly, this protocol is easily adapted to the selective one-pot synthesis of the corresponding γ-dihalomethylidenated enals in up to 49 % overall yield. Mechanistic studies are in favor of a radical chain propagation initiated by an oxidative quenching of the photocatalyst.

Organophotocatalytic Regioselective Silylation/Germylation and Cascade Cyclization of N-Alkenyl α-CF3 Acrylamides: Access to Densely Functionalized 4-Pyrrolin-2-ones

We report an organophotoredox-catalyzed silylation/germylation cascade cyclization of N-alkenyl α-CF3 acrylamides under mild conditions. N-Aminopyridinium salts act as hydrogen atom transfer reagents under photoredox catalysis in the generation of silyl and germyl radicals. An array of silyl- and germyl-substituted 3-CF3-4-pyrrolin-2-one derivatives were constructed in a shorter reaction time with low catalyst loading in good to excellent yields at room temperature. Importantly, this protocol is amenable to the late-stage diversification of bioactive molecules, as well as to large-scale synthesis.

Electrochemical Benzylic C-H Amination via N-Aminopyridinium

An electrochemical protocol for benzylic C(sp3)-H aminopyridylation via direct C-H/N-H cross-coupling of alkylarenes with N-aminopyridinium triflate has been developed. This method features excellent site-selectivity, broad substrate scope, redox reagent-free and facile scalability. The generated benzylaminopyridiniums can be readily converted to benzylamines via electroreductive N-N bond cleavage.

N-Iminopyridinium Compounds in Giese Reaction: Photoinduced Homolytic N-N and C-C Bond Cleavage for Cyanoalkyl Radical Generation

We present an innovative photoinduced cyanoalkyl radical addition methodology using N-iminopyridinium reagents derived from cyclic ketones. Mechanistic investigations reveal the association of the excited Hantzsch ester and iminopyridinium with pyridyl radical generation. The ensuing cascade involving homolytic N-N bond and C-C bond cleavage of the pyridyl radical ultimately leads to the formation of cyanoalkyl radical species, leading to diverse Giese-type products. The method showcases versatility and synthetic utility in late-stage functionalization.

Electrophilic Fluorination of Silyl Dienol Ethers: a General and Selective Access to γ-Fluoro Enals

We describe the direct synthesis of γ-fluoro enals from the corresponding silyl dienol ethers. This simple process operates under mild conditions and is compatible with a wide range of functionalities. The high γ regioselectivity of this protocol was rationalized by means of theoretical calculations.

Visible-Light-Induced Radical Cascade Cross-Coupling via C(sp3)-H Activation and C-N/N-O Cleavage: Feasible Access to Methylenebisamide Derivatives

Here we report facile and manipulable access to methylenebisamide derivatives via visible-light-driven radical cascade processes incorporating C(sp³)-H activation and C-N/N-O cleavage. Mechanistic studies reveal that a traditional Ir-catalyzed photoredox pathway and a novel copper-induced complex-photolysis pathway are both involved, contributing to activating the inert N-methoxyamides and rendering the valuable bisamides. This approach exhibits many advantages, including mild reaction conditions, broad scope and functional group tolerance, and competitive step economy. Given the mechanistic plenitude and operational simplicity, we believe this package deal paves a promising way for the synthesis of valuable nitrogen-containing molecules.

Highly selective γ-alkoxylation, γ-amination and γ-alkylation of unbiased enals by means of photoredox catalysis

We report herein a general and highly selective γ-functionalization protocol under visible light irradiation. This mild radical approach enables the expansion of the scope of application to unbiased enals and the introduction of a wide variety of alkoxy, amino and alkyl functionalities in the γ position with complete regioselectivity.