Photocatalytic Aerobic Cyclization of N-Propargylamides Enabled by Selenium-π-Acid Catalysis.

A dual catalytic approach combining photocatalyst and selenium-π-acid synergy has been used to cyclized of N-propargylamides. This method offers readily access to oxazole aldehydes under chemical oxidant-free conditions with low catalyst loadings, where air acts as a terminal and gratuitous oxidant. The reaction is demonstrated with a range of substrates, including aryl and alkyl propargyl amides, and in the late-stage functionalization of several amide-containing drug molecules. Mechanistic studies suggest that the acridinium catalyst is able to oxidize diselenide and generate singlet oxygen (1 O2 ), which is responsible for this transformation.

Oxidative Three-Component Selenofunctionalization of Alkenes: Convenient Access to Vicinally Functionalized Selenides.

Three-component selenofunctionalization processes of olefins, diselenides and sulfonamides, water, alcohols, or acids utilizing 1-fluoropyridinium triflate (FP-OTf) as a reaction promoter are reported. Under the optimal conditions, a broad range of vicinally functionalized selenide derivatives was accessible with high yields and excellent functional group compatibilities. Mechanistic studies revealed that the FP-OTf played a key role in this selenofunctionalization process.

N-Fluorobenzenesulfonimide-Mediated Intermolecular Carboselenenylation of Olefins with Aromatics and Diselenides.

Intermolecular carboselenenylation of easily accessible alkenes by utilizing diselenides and N-fluorobenzenesulfonimide (NFSI) under metal-free and mild conditions is reported. Preliminary mechanistic studies indicate that the oxidation of diselenide by NFSI through a single-electron-transfer process produces an active selenenyl cationic radical species that initiates the intermolecular carboselenenylation of olefins, forming key Se-C and C-C bonds. Under optimized conditions, a broad spectrum of functionally and structurally diverse selenoether derivatives with promising yields is accessed with a very high functional group tolerance.

Iodine pentoxide-mediated oxidative selenation and seleno/thiocyanation of electron-rich arenes.

A simple and efficient method for the regioselective selenation of electron-rich arenes by employing non-metal inorganic iodine pentoxide (I2O5) as a reaction promoter under ambient conditions has been developed. The present protocol showed broad functional group tolerance and easy-to-operate and time-economical features. Additionally, this protocol also allows access to 3-seleno and 3-thiocyanoindoles by the use of readily available selenocyanate and thiocyanate salts. A mechanistic study indicated that the transformation operated through selenenyl iodide-induced electrophilic substitution processes.

Photoinduced Intermolecular Hydroamination and Hydroetherification of Electron-rich Alkenes with Low Catalyst Loadings.

A photochemical method based on visible-light irradiation (blue LEDs/sunlight) has been developed for the intermolecular hydroamination and hydroetherification of electron-rich alkenes. This photochemical method is compatible with a wide range of azoles and electron-rich alkenes, such as vinyl ethers, vinyl sulfides and enamides, and is performed with low concentrations of photocatalyst (1000 ppm). Comprehensive mechanistic studies indicate that this process is initiated by the formation of an active radical cation intermediate through single electron oxidation of azole, which is mediated by excited Acr-Mes+ BF4-.