Benzeneseleninic Acid in the Photo-Catalyzed Hydroxy-Selenylation of Styrenes

Abstract

We established a new visible-light-mediated protocol for the regioselective βhydroxyselenylation of olefins, employing benzeneseleninic acid as substrate. Regarding a novel approach, the benzeneseleninic acid emerges as an efficient and affordable reagent to be used as an electrophilic selenium source that can be easily converted to selenium-based radical species under visible-light conditions. In this sense, the photocatalytically formed PhSe• radical can react directly with unsaturated substrates, including alkenes, to access a new C-Se bond and a carbon-centered radical intermediate, which finally is trapped by a hydroxyl radical species, delivering the βhydroxyselanyl compounds. Thus, despite the versatile utilities in organic synthesis, such as building blocks, the β-hydroxyselanyl compounds have demonstrated important biological activities. Based on that, we concentrated our efforts on developing a robust, effective, and environmentally benign methodology for their preparation. The optimal condition involves the reaction between styrene and 1.0 equivalent of phenylseleninic acid, in the presence of 5.0 mol% of eosin Y, as a cheap and easily available photocatalyst, with DMSO promoting the reaction medium. Satisfactorily, the system was irradiated with blue LED light for 2 h, to deliver the desired products in good yields.

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

“…In contrast to the electrophilic activation strategy, the mechanistically distinct selenofunctionalization of alkenes has been explored by generating the selenium radical species under electrochemical and photochemical conditions (Scheme b). In addition, different photocatalysts have been successfully utilized for the oxyselenylation, aminoselenylation, and selenoarylation of alkenes under visible light conditions, where the photochemically generated PhSe· radicals were oxidized to the PhSe+ cation by molecular oxygen. While the generation of PhSe+ cationic species via the photochemical activation of diselenides under air might be a valid mechanistic interpretation in electron-rich alkenes, − a recent study by Liu and Ling demonstrated an alternative reaction pathway for the visible-light-induced oxidative coupling of alkenes and diselenides, involving the PhSe· radical addition to alkenes followed by trapping the carbon-based radicals with molecular oxygen to give α-aryl selenomethyl ketones .…”

“…In addition, different photocatalysts have been successfully utilized for the oxyselenylation, aminoselenylation, and selenoarylation of alkenes under visible light conditions, where the photochemically generated PhSe· radicals were oxidized to the PhSe+ cation by molecular oxygen. While the generation of PhSe+ cationic species via the photochemical activation of diselenides under air might be a valid mechanistic interpretation in electron-rich alkenes, − a recent study by Liu and Ling demonstrated an alternative reaction pathway for the visible-light-induced oxidative coupling of alkenes and diselenides, involving the PhSe· radical addition to alkenes followed by trapping the carbon-based radicals with molecular oxygen to give α-aryl selenomethyl ketones . Inspired by the photochemical generation of selenium radical species under visible light conditions, a radical selenofunctionalization of alkenes was envisioned as a unified way of introducing multiple functional groups under aerobic conditions (Scheme c).…”