Visible-Light-Promoted Aryl Cation Formation: Aromatic SN1 Reactions of Areneazo-2-(2-nitro)propanes.

The visible light excitation of areneazo-2-(2-nitro)propane·HCl salts generated the singlet aryl cation that readily underwent aromatic SN1 reactions with a variety of nucleophiles. The in situ generated singlet aryl cation was stabilized by a counter nitronate anion that prevented other intersystem crossing and single electron transfer processes. With the improved safety features of neutral areneazo-2-(2-nitro)propane derivatives, the current visible-light-promoted aromatic SN1 reactions provide an alternative aryl Csp2-X bond forming strategy.

Visible-Light-Induced Three-Component Selenofunctionalization of Alkenes: An Aerobic Selenol Oxidation Approach.

A photocatalyst-free visible-light-induced selenofunctionalization of alkenes has been developed using a variety of nucleophiles. The homolytic scission of diselenides under visible-light conditions coupled with the aerobic selenol oxidation to diselenides allowed the successful implementation of three-component selenofunctionalization under visible-light irradiation in open-air conditions. The mechanistic studies revealed the critical role of oxygen content in a reaction medium, where the electron transfer process from the carbon-based radicals to either molecular oxygen or selenyl radicals was controlled.

Visible-Light-Promoted Photoaddition of N-Nitrosopiperidines to Alkynes: Continuous Flow Chemistry Approach to Tetrahydroimidazo[1,2-a]pyridine 1-Oxides.

The photoaddition of N-nitrosopiperidines to terminal alkynes was effected under visible-light irradiation, in which a novel synthetic access to tetrahydroimidazo[1,2-a]pyridine 1-oxides was achieved via the dehydrogenative cycloisomerization of ß-nitroso enamine intermediates. The decomposition pathways of N-nitrosamines, alkynes, and ß-nitroso enamine intermediates were better handled in a continuous flow setting through the diffusion control of chemical species that negatively affected the formation of tetrahydroimidazo[1,2-a]pyridine 1-oxides under batch reaction conditions.

Dimeric-serotonin bivalent ligands induced gold nanoparticle aggregation for highly sensitive and selective serotonin biosensor.

Chemically modulating monoamine neurotransmitter serotonin undergoes a physiological reaction of enzyme intermediated peroxidation to reconstruct dimeric self-assembled complex. A standard bivalent ligand approach dimeric serotonin increases structural and functional scaffolding with recognition-binding sites that are fundamentally more friendly than monovalent binding sites. Dimerization reaction accelerates the catalytic activity of one-electron oxidation at the C(4) position of serotonin to generate dual phenolic radicals in the presence of horseradish (HRP) and hydrogen peroxide (H2O2). Herein, we suggest the dimeric serotonin-based colorimetric assay, which presents a new rapid, sensitive, selective, and quantitative visualization. The dimeric serotonin possesses the capability to recognize intermolecular interaction units that cause aggregation scaffold of gold nanoparticles (GNPs), providing inexpensive and straightforward analytical needs. As a proof of visual and spectral analysis, peroxidative dimeric serotonin demonstrated sensitive and robust results. The calorimetric method enables highly sensitive detection of serotonin in phosphate buffer, and in human serum samples at nanomolar levels with a LOD of 2.6 nM and 2.81 nM, respectively, and the sensor possesses a dynamic range of 100-300 nM in buffer condition. Also, as proof of concept, visible color imaging of immunosensors which is appropriate for fast visible testing at detection limits as low as 2.90 nM concentration.

Visible-Light-Induced Photoaddition of N-Nitrosoalkylamines to Alkenes: One-Pot Tandem Approach to 1,2-Diamination of Alkenes from Secondary Amines.

The generation of aminium radical cation species from N-nitrosoamines is disclosed for the first time through visible-light excitation at 453 nm. The developed visible-light-promoted photoaddition reaction of N-nitrosoamines to alkenes was combined with the o-NQ-catalyzed aerobic oxidation protocol of amines to telescope the direct handling of harmful N-nitroso compounds, where the desired α-amino oxime derivatives were obtained in a one-pot tandem N-nitrosation and photoaddition sequence.

Visible Light-Promoted Friedel-Crafts-Type Chloroacylation of Alkenes to ß-Chloroketones.

The photoredox chloroacylation of alkenes has been developed as a substitute for the Friedel-Crafts acylation of alkenes to ß-chloroketones. The direct generation of acyl radical species from acid chlorides under the photoredox conditions allows the formation of ß-chloroketones without dehydrochlorination with the help of KHCO3. The synthetic utility of the current method is demonstrated in the one-pot synthesis of dihydroisoxazole, dihydropyrazole, and dihydropyrimidine-2-thione in 1 mmol scale.

ß-Oxidation of Ynamides into N,O-Acetals by mCPBA: Application in Enantioselective Intermolecular Transacetalization.

Oxidation of ynamides by mCPBA led to ß-oxygenation and resulted in formation of carbonyl compounds with α-N,O-acetal functionality. These N,O-acetals are formed in high yields and can be stored indefinitely at room temperature. Yet, they can be activated by a chiral Brønsted acid and underwent an enantioselective transacetalization into a α-N,O-acetal. Subsequent diastereoselective transformations occurred with exceptional selectivity according to Felkin-Anh model.

Visible-Light-Promoted Thiyl Radical Generation from Sodium Sulfinates: A Radical-Radical Coupling to Thioesters.

A convenient visible-light photoredox catalysis has been developed for the synthesis of thioesters from two readily available starting materials: acid chlorides and sodium sulfinates. The facile generation of acyl radical species under the visible light photoredox conditions allows the formation of thiyl radical species from sodium sulfinates via multiple single electron transfer reactions, where the final acyl radical-thiyl radical coupling has been accomplished. The direct radical-radical coupling strategy offers a mild and controlled photochemical approach to important synthetic building blocks such as thioesters.

Brønsted Acid Catalyzed Oxygenative Bimolecular Friedel-Crafts-type Coupling of Ynamides.

A non-metal approach for accessing α-oxo carbene surrogates for a C-C bond-forming bimolecular coupling between ynamides and nucleophilic arenes was developed. This acid-catalyzed coupling features mild temperature, which is critical for the required temporal chemoselectivity among nucleophiles. The scope of nucleophiles includes indoles, pyrroles, anilines, phenols and silyl enolethers. Furthermore, a direct test of SN 2' mechanism has been provided by employing chiral N,N'-dioxides which also enlightens the nature of the intermediates in related metal-catalyzed processes.

Aerobic oxygenative cleavage of electron deficient C-C triple bonds in the gold-catalyzed cyclization of 1,6-enynes.

Gold-catalyzed aerobic oxygenative cleavage of triple bonds that occurs under the ambient pressure of air and at room temperature is reported; radical inhibition tests suggest that oxygenation occurs via a gold-bound metalloradical intermediate.