Radical Cation Cycloadditions Using Cleavable Redox Auxiliaries

Abstract

The incorporation of an easily oxidized arylsulfide moiety facilitates the photocatalytic generation of alkene radical cations that undergo a variety of cycloaddition reactions with electron-rich reaction partners. The sulfide moiety can subsequently be reductively cleaved in a traceless fashion, affording products that are not otherwise directly accessible using photoredox catalysis. This approach constitutes a novel oxidative “redox auxiliary” strategy that offers a practical means to circumvent a fundamental thermodynamic limitation facing photoredox reactions.

Stepwise radical cation Diels–Alder reaction via multiple pathways

“…Although most recent examples of the radical cation Diels–Alder reaction have employed styrenes, the scope is not limited to such electron-rich dienophiles. Bauld and Yoon demonstrated that aryl vinyl ethers, enol ether equivalents, and aryl vinyl sulfides are also promising dienophiles for the reactions ( Scheme 2 ) [ 17 , 20 – 25 ].…”

Deal;Photoredox Catalysis for the Cycloaddition Reactions

“…In 2016, Yoon and co-workers reported a photooxidative cycloaddition system with the addition of cleavable redox auxiliaries. [76] To extend the scope of the substrates for electronically mismatched [4 + 2] cycloaddition reactions, aryl vinyl sulfides as redox auxiliaries were introduced to alkene substrates, which were not able to undergo single electron transfer mechanism, and these redox auxiliaries were easily cleaved by the treatment with Raney nickel after affording the desired cycloadducts. Interestingly, acyclic and simple cyclic dienes worked well under this condition, although some sterically bulky dienes proceeded sluggishly (Scheme 23).…”

Stereoretention in Styrene Heterodimerisation Promoted by One-Electron Oxidants

“…C-X bonds. [32][33][34][35][36][37] Their formation is typically achieved via single-electron transfer (SET) from a neutral substrate's p-bond or lone-pair, creating a "hole" in the system. This process can be mediated using transition metals, either by themselves 7,[38][39][40] or coupled with organic 41 or organometallic [42][43][44][45] photoredox catalysts; it can also be mediated by organic oxidants such as aminium radical cationic salts.…”